Issue %3005 - Move modules/libpref to components/preferences

- greprefs is now in system/

17 files changed, 6517 insertions, 0 deletions

diff --git a/components/preferences/moz.build b/components/preferences/moz.build
index 635fa39c9..4bd147384 100644
--- a/components/preferences/moz.build
+++ b/components/preferences/moz.build
@@ -3,4 +3,30 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+include('/ipc/chromium/chromium-config.mozbuild')
+
+DEFINES['OS_ARCH'] = CONFIG['OS_ARCH']
+DEFINES['MOZ_WIDGET_TOOLKIT'] = CONFIG['MOZ_WIDGET_TOOLKIT']
+
+XPIDL_SOURCES += [
+  'public/nsIPrefBranch.idl',
+  'public/nsIPrefBranch2.idl',
+  'public/nsIPrefBranchInternal.idl',
+  'public/nsIPrefLocalizedString.idl',
+  'public/nsIPrefService.idl',
+  'public/nsIRelativeFilePref.idl',
+]
+
+EXPORTS.mozilla += ['src/Preferences.h']
+
+SOURCES += [
+  'src/nsPrefBranch.cpp',
+  'src/nsPrefsFactory.cpp',
+  'src/prefapi.cpp',
+  'src/Preferences.cpp',
+  'src/prefread.cpp',
+]
+
+XPIDL_MODULE = 'pref'
+FINAL_LIBRARY = 'xul'
 JAR_MANIFESTS += ['jar.mn']
\ No newline at end of file
diff --git a/components/preferences/public/nsIPrefBranch.idl b/components/preferences/public/nsIPrefBranch.idl
new file mode 100644
index 000000000..900806b42
--- /dev/null
+++ b/components/preferences/public/nsIPrefBranch.idl
@@ -0,0 +1,425 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIObserver;
+
+/**
+ * The nsIPrefBranch interface is used to manipulate the preferences data. This
+ * object may be obtained from the preferences service (nsIPrefService) and
+ * used to get and set default and/or user preferences across the application.
+ *
+ * This object is created with a "root" value which describes the base point in
+ * the preferences "tree" from which this "branch" stems. Preferences are
+ * accessed off of this root by using just the final portion of the preference.
+ * For example, if this object is created with the root "browser.startup.",
+ * the preferences "browser.startup.page", "browser.startup.homepage",
+ * and "browser.startup.homepage_override" can be accessed by simply passing
+ * "page", "homepage", or "homepage_override" to the various Get/Set methods.
+ *
+ * @see nsIPrefService
+ */
+
+[scriptable, uuid(55d25e49-793f-4727-a69f-de8b15f4b985)]
+interface nsIPrefBranch : nsISupports
+{
+
+  /**
+   * Values describing the basic preference types.
+   *
+   * @see getPrefType
+   */
+  const long PREF_INVALID = 0;
+  const long PREF_STRING = 32;
+  const long PREF_INT = 64;
+  const long PREF_BOOL = 128;
+
+  /**
+   * Called to get the root on which this branch is based, such as
+   * "browser.startup."
+   */
+  readonly attribute string root;
+
+  /**
+   * Called to determine the type of a specific preference.
+   *
+   * @param aPrefName The preference to get the type of.
+   *
+   * @return long     A value representing the type of the preference. This
+   *                  value will be PREF_STRING, PREF_INT, or PREF_BOOL.
+   */
+  long getPrefType(in string aPrefName);
+
+  /**
+   * Called to get the state of an individual boolean preference.
+   *
+   * @param aPrefName The boolean preference to get the state of.
+   * @param aDefaultValue The value to return if the preference is not set.
+   *
+   * @return boolean  The value of the requested boolean preference.
+   *
+   * @see setBoolPref
+   */
+  [optional_argc,binaryname(GetBoolPrefWithDefault)]
+  boolean getBoolPref(in string aPrefName, [optional] in boolean aDefaultValue);
+  [noscript,binaryname(GetBoolPref)]
+  boolean getBoolPrefXPCOM(in string aPrefName);
+
+  /**
+   * Called to set the state of an individual boolean preference.
+   *
+   * @param aPrefName The boolean preference to set the state of.
+   * @param aValue    The boolean value to set the preference to.
+   *
+   * @throws Error if setting failed or the preference has a default
+             value of a type other than boolean.
+   *
+   * @see getBoolPref
+   */
+  void setBoolPref(in string aPrefName, in boolean aValue);
+
+  /**
+   * Called to get the state of an individual floating-point preference.
+   * "Floating point" preferences are really string preferences that
+   * are converted to floating point numbers.
+   *
+   * @param aPrefName The floating point preference to get the state of.
+   * @param aDefaultValue The value to return if the preference is not set.
+   *
+   * @return float  The value of the requested floating point preference.
+   *
+   * @see setCharPref
+   */
+  [optional_argc,binaryname(GetFloatPrefWithDefault)]
+  float getFloatPref(in string aPrefName, [optional] in float aDefaultValue);
+  [noscript,binaryname(GetFloatPref)]
+  float getFloatPrefXPCOM(in string aPrefName);
+
+  /**
+   * Called to get the state of an individual string preference.
+   *
+   * @param aPrefName The string preference to retrieve.
+   * @param aDefaultValue The string to return if the preference is not set.
+   *
+   * @return string   The value of the requested string preference.
+   *
+   * @see setCharPref
+   */
+  [optional_argc,binaryname(GetCharPrefWithDefault)]
+  string getCharPref(in string aPrefName, [optional] in string aDefaultValue);
+  [noscript,binaryname(GetCharPref)]
+  string getCharPrefXPCOM(in string aPrefName);
+
+  /**
+   * Called to set the state of an individual string preference.
+   *
+   * @param aPrefName The string preference to set.
+   * @param aValue    The string value to set the preference to.
+   *
+   * @throws Error if setting failed or the preference has a default
+             value of a type other than string.
+   *
+   * @see getCharPref
+   */
+  void setCharPref(in string aPrefName, in string aValue);
+
+  /**
+   * Called to get the state of an individual integer preference.
+   *
+   * @param aPrefName The integer preference to get the value of.
+   * @param aDefaultValue The value to return if the preference is not set.
+   *
+   * @return long     The value of the requested integer preference.
+   *
+   * @see setIntPref
+   */
+  [optional_argc,binaryname(GetIntPrefWithDefault)]
+  long getIntPref(in string aPrefName, [optional] in long aDefaultValue);
+  [noscript,binaryname(GetIntPref)]
+  long getIntPrefXPCOM(in string aPrefName);
+
+  /**
+   * Called to set the state of an individual integer preference.
+   *
+   * @param aPrefName The integer preference to set the value of.
+   * @param aValue    The integer value to set the preference to.
+   *
+   * @throws Error if setting failed or the preference has a default
+             value of a type other than integer.
+   *
+   * @see getIntPref
+   */
+  void setIntPref(in string aPrefName, in long aValue);
+
+  /**
+   * Called to get the state of an individual complex preference. A complex
+   * preference is a preference which represents an XPCOM object that can not
+   * be easily represented using a standard boolean, integer or string value.
+   *
+   * @param aPrefName The complex preference to get the value of.
+   * @param aType     The XPCOM interface that this complex preference
+   *                  represents. Interfaces currently supported are:
+   *                    - nsIFile
+   *                    - nsISupportsString (UniChar)
+   *                    - nsIPrefLocalizedString (Localized UniChar)
+   * @param aValue    The XPCOM object into which to the complex preference 
+   *                  value should be retrieved.
+   *
+   * @throws Error The value does not exist or is the wrong type.
+   *
+   * @see setComplexValue
+   */
+  void getComplexValue(in string aPrefName, in nsIIDRef aType,
+                       [iid_is(aType), retval] out nsQIResult aValue);
+
+  /**
+   * Called to set the state of an individual complex preference. A complex
+   * preference is a preference which represents an XPCOM object that can not
+   * be easily represented using a standard boolean, integer or string value.
+   *
+   * @param aPrefName The complex preference to set the value of.
+   * @param aType     The XPCOM interface that this complex preference
+   *                  represents. Interfaces currently supported are:
+   *                    - nsIFile
+   *                    - nsISupportsString (UniChar)
+   *                    - nsIPrefLocalizedString (Localized UniChar)
+   * @param aValue    The XPCOM object from which to set the complex preference 
+   *                  value.
+   *
+   * @throws Error if setting failed or the value is the wrong type.
+   *
+   * @see getComplexValue
+   */
+  void setComplexValue(in string aPrefName, in nsIIDRef aType, in nsISupports aValue);
+
+  /**
+   * Called to clear a user set value from a specific preference. This will, in
+   * effect, reset the value to the default value. If no default value exists
+   * the preference will cease to exist.
+   *
+   * @param aPrefName The preference to be cleared.
+   *
+   * @note
+   * This method does nothing if this object is a default branch.
+   */
+  void clearUserPref(in string aPrefName);
+
+  /**
+   * Called to lock a specific preference. Locking a preference will cause the
+   * preference service to always return the default value regardless of
+   * whether there is a user set value or not.
+   *
+   * @param aPrefName The preference to be locked.
+   *
+   * @note
+   * This method can be called on either a default or user branch but, in
+   * effect, always operates on the default branch.
+   *
+   * @throws Error The preference does not exist or an error occurred.
+   *
+   * @see unlockPref
+   */
+  void lockPref(in string aPrefName);
+
+  /**
+   * Called to check if a specific preference has a user value associated to
+   * it.
+   *
+   * @param aPrefName The preference to be tested.
+   *
+   * @note
+   * This method can be called on either a default or user branch but, in
+   * effect, always operates on the user branch.
+   *
+   * @note
+   * If a preference was manually set to a value that equals the default value,
+   * then the preference no longer has a user set value, i.e. it is
+   * considered reset to its default value.
+   * In particular, this method will return false for such a preference and
+   * the preference will not be saved to a file by nsIPrefService.savePrefFile.
+   *
+   * @return boolean  true  The preference has a user set value.
+   *                  false The preference only has a default value.
+   */
+  boolean prefHasUserValue(in string aPrefName);
+
+  /**
+   * Called to check if a specific preference is locked. If a preference is
+   * locked calling its Get method will always return the default value.
+   *
+   * @param aPrefName The preference to be tested.
+   *
+   * @note
+   * This method can be called on either a default or user branch but, in
+   * effect, always operates on the default branch.
+   *
+   * @return boolean  true  The preference is locked.
+   *                  false The preference is not locked.
+   *
+   * @see lockPref
+   * @see unlockPref
+   */
+  boolean prefIsLocked(in string aPrefName);
+
+  /**
+   * Called to unlock a specific preference. Unlocking a previously locked 
+   * preference allows the preference service to once again return the user set
+   * value of the preference.
+   *
+   * @param aPrefName The preference to be unlocked.
+   *
+   * @note
+   * This method can be called on either a default or user branch but, in
+   * effect, always operates on the default branch.
+   *
+   * @throws Error The preference does not exist or an error occurred.
+   *
+   * @see lockPref
+   */
+  void    unlockPref(in string aPrefName);
+
+
+  /**
+   * Called to remove all of the preferences referenced by this branch.
+   *
+   * @param aStartingAt The point on the branch at which to start the deleting
+   *                    preferences. Pass in "" to remove all preferences
+   *                    referenced by this branch.
+   *
+   * @note
+   * This method can be called on either a default or user branch but, in
+   * effect, always operates on both.
+   *
+   * @throws Error The preference(s) do not exist or an error occurred.
+   */
+  void deleteBranch(in string aStartingAt);
+
+  /**
+   * Returns an array of strings representing the child preferences of the
+   * root of this branch.
+   * 
+   * @param aStartingAt The point on the branch at which to start enumerating
+   *                    the child preferences. Pass in "" to enumerate all
+   *                    preferences referenced by this branch.
+   * @param aCount      Receives the number of elements in the array.
+   * @param aChildArray Receives the array of child preferences.
+   *
+   * @note
+   * This method can be called on either a default or user branch but, in
+   * effect, always operates on both.
+   *
+   * @throws Error The preference(s) do not exist or an error occurred.
+   */
+  void getChildList(in string aStartingAt,
+                    [optional] out unsigned long aCount,
+                    [array, size_is(aCount), retval] out string aChildArray);
+
+  /**
+   * Called to reset all of the preferences referenced by this branch to their
+   * default values.
+   *
+   * @param aStartingAt The point on the branch at which to start the resetting
+   *                    preferences to their default values. Pass in "" to
+   *                    reset all preferences referenced by this branch.
+   *
+   * @note
+   * This method can be called on either a default or user branch but, in
+   * effect, always operates on the user branch.
+   *
+   * @throws Error The preference(s) do not exist or an error occurred.
+   */
+  void resetBranch(in string aStartingAt);
+
+  /**
+   * Add a preference change observer. On preference changes, the following
+   * arguments will be passed to the nsIObserver.observe() method:
+   *   aSubject - The nsIPrefBranch object (this)
+   *   aTopic   - The string defined by NS_PREFBRANCH_PREFCHANGE_TOPIC_ID
+   *   aData    - The name of the preference which has changed, relative to
+   *              the |root| of the aSubject branch.
+   *
+   * aSubject.get*Pref(aData) will get the new value of the modified
+   * preference. For example, if your observer is registered with
+   * addObserver("bar.", ...) on a branch with root "foo.", modifying
+   * the preference "foo.bar.baz" will trigger the observer, and aData
+   * parameter will be "bar.baz".
+   *
+   * @param aDomain   The preference on which to listen for changes. This can
+   *                  be the name of an entire branch to observe.
+   *                  e.g. Holding the "root" prefbranch and calling
+   *                  addObserver("foo.bar.", ...) will observe changes to
+   *                  foo.bar.baz and foo.bar.bzip
+   * @param aObserver The object to be notified if the preference changes.
+   * @param aHoldWeak true  Hold a weak reference to |aObserver|. The object
+   *                        must implement the nsISupportsWeakReference
+   *                        interface or this will fail.
+   *                  false Hold a strong reference to |aObserver|.
+   *
+   * @note
+   * Registering as a preference observer can open an object to potential
+   * cyclical references which will cause memory leaks. These cycles generally
+   * occur because an object both registers itself as an observer (causing the
+   * branch to hold a reference to the observer) and holds a reference to the
+   * branch object for the purpose of getting/setting preference values. There
+   * are 3 approaches which have been implemented in an attempt to avoid these
+   * situations.
+   * 1) The nsPrefBranch object supports nsISupportsWeakReference. Any consumer
+   *    may hold a weak reference to it instead of a strong one.
+   * 2) The nsPrefBranch object listens for xpcom-shutdown and frees all of the
+   *    objects currently in its observer list. This ensures that long lived
+   *    objects (services for example) will be freed correctly.
+   * 3) The observer can request to be held as a weak reference when it is
+   *    registered. This insures that shorter lived objects (say one tied to an
+   *    open window) will not fall into the cyclical reference trap.
+   *
+   * @note
+   * The list of registered observers may be changed during the dispatch of
+   * nsPref:changed notification. However, the observers are not guaranteed
+   * to be notified in any particular order, so you can't be sure whether the
+   * added/removed observer will be called during the notification when it
+   * is added/removed.
+   *
+   * @note
+   * It is possible to change preferences during the notification.
+   *
+   * @note
+   * It is not safe to change observers during this callback in Gecko 
+   * releases before 1.9. If you want a safe way to remove a pref observer,
+   * please use an nsITimer.
+   *
+   * @see nsIObserver
+   * @see removeObserver
+   */
+  void addObserver(in string aDomain, in nsIObserver aObserver,
+                   in boolean aHoldWeak);
+
+  /**
+   * Remove a preference change observer.
+   *
+   * @param aDomain   The preference which is being observed for changes.
+   * @param aObserver An observer previously registered with addObserver().
+   *
+   * @note
+   * Note that you must call removeObserver() on the same nsIPrefBranch
+   * instance on which you called addObserver() in order to remove aObserver;
+   * otherwise, the observer will not be removed.
+   *
+   * @see nsIObserver
+   * @see addObserver
+   */
+  void removeObserver(in string aDomain, in nsIObserver aObserver);
+};
+
+
+%{C++
+
+#define NS_PREFBRANCH_CONTRACTID "@mozilla.org/preferencesbranch;1"
+/**
+ * Notification sent when a preference changes.
+ */
+#define NS_PREFBRANCH_PREFCHANGE_TOPIC_ID "nsPref:changed"
+
+%}
diff --git a/components/preferences/public/nsIPrefBranch2.idl b/components/preferences/public/nsIPrefBranch2.idl
new file mode 100644
index 000000000..f1087c92d
--- /dev/null
+++ b/components/preferences/public/nsIPrefBranch2.idl
@@ -0,0 +1,16 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIPrefBranch.idl"
+
+/**
+ * An empty interface to provide backwards compatibility for existing code.
+ *
+ * @see nsIPrefBranch
+ */
+[scriptable, uuid(8892016d-07f7-4530-b5c1-d73dfcde4a1c)]
+interface nsIPrefBranch2 : nsIPrefBranch
+{
+};
diff --git a/components/preferences/public/nsIPrefBranchInternal.idl b/components/preferences/public/nsIPrefBranchInternal.idl
new file mode 100644
index 000000000..476e6a59f
--- /dev/null
+++ b/components/preferences/public/nsIPrefBranchInternal.idl
@@ -0,0 +1,17 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsIPrefBranch2.idl"
+
+/**
+ * An empty interface to provide backwards compatibility for existing code that
+ * bsmedberg didn't want to break all at once. Don't use me!
+ *
+ * @status NON-FROZEN interface WHICH WILL PROBABLY GO AWAY.
+ */
+
+[scriptable, uuid(355bd1e9-248a-438b-809d-e0db1b287882)]
+interface nsIPrefBranchInternal : nsIPrefBranch2
+{
+};
diff --git a/components/preferences/public/nsIPrefLocalizedString.idl b/components/preferences/public/nsIPrefLocalizedString.idl
new file mode 100644
index 000000000..f99d60f6f
--- /dev/null
+++ b/components/preferences/public/nsIPrefLocalizedString.idl
@@ -0,0 +1,64 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+/**
+ * The nsIPrefLocalizedString interface is simply a wrapper interface for
+ * nsISupportsString so the preferences service can have a unique identifier
+ * to distinguish between requests for normal wide strings (nsISupportsString)
+ * and "localized" wide strings, which get their default values from properites
+ * files.
+ *
+ * @see nsIPrefBranch
+ * @see nsISupportsString
+ */
+
+[scriptable, uuid(ae419e24-1dd1-11b2-b39a-d3e5e7073802)]
+interface nsIPrefLocalizedString : nsISupports
+{
+  /**
+   * Provides access to string data stored in this property.
+   *
+   * @throws Error An error occurred.
+   */
+  attribute wstring data;
+
+  /**
+   * Used to retrieve the contents of this object into a wide string.
+   *
+   * @return wstring The string containing the data stored within this object.
+   */
+  wstring toString();
+
+  /**
+   * Used to set the contents of this object.
+   *
+   * @param length The length of the string. This value should not include
+   *               space for the null terminator, nor should it account for the
+   *               size of a character. It should  only be the number of
+   *               characters for which there is space in the string.
+   * @param data   The string data to be stored.
+   *
+   * @note
+   * This makes a copy of the string argument passed in.
+   */
+  void setDataWithLength(in unsigned long length,
+                         [size_is(length)] in wstring data);
+};
+
+%{C++
+
+#define NS_PREFLOCALIZEDSTRING_CID                     \
+  { /* {064d9cee-1dd2-11b2-83e3-d25ab0193c26} */       \
+    0x064d9cee,                                        \
+    0x1dd2,                                            \
+    0x11b2,                                            \
+    { 0x83, 0xe3, 0xd2, 0x5a, 0xb0, 0x19, 0x3c, 0x26 } \
+  }
+
+#define NS_PREFLOCALIZEDSTRING_CONTRACTID "@mozilla.org/pref-localizedstring;1"
+
+%}
diff --git a/components/preferences/public/nsIPrefService.idl b/components/preferences/public/nsIPrefService.idl
new file mode 100644
index 000000000..0db401996
--- /dev/null
+++ b/components/preferences/public/nsIPrefService.idl
@@ -0,0 +1,160 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+#include "nsIPrefBranch.idl"
+
+%{C++
+struct PrefTuple;
+#include "nsTArrayForwardDeclare.h"
+%}
+
+[ptr] native nsPreferencesArrayPtr(nsTArray<PrefTuple>);
+[ptr] native nsPreferencePtr(PrefTuple);
+[ptr] native nsPreferencePtrConst(const PrefTuple);
+
+interface nsIFile;
+
+/**
+ * The nsIPrefService interface is the main entry point into the back end
+ * preferences management library. The preference service is directly
+ * responsible for the management of the preferences files and also facilitates
+ * access to the preference branch object which allows the direct manipulation
+ * of the preferences themselves.
+ *
+ * @see nsIPrefBranch
+ */
+
+[scriptable, uuid(1f84fd56-3956-40df-b86a-1ea01402ee96)]
+interface nsIPrefService : nsISupports
+{
+  /**
+   * Called to read in the preferences specified in a user preference file.
+   *
+   * @param aFile The file to be read.
+   *
+   * @note
+   * If nullptr is passed in for the aFile parameter the default preferences
+   * file(s) [prefs.js, user.js] will be read and processed.
+   *
+   * @throws Error File failed to read or contained invalid data.
+   *
+   * @see savePrefFile
+   * @see nsIFile
+   */
+  void readUserPrefs(in nsIFile aFile);
+
+  /**
+   * Called to completely flush and re-initialize the preferences system.
+   *
+   * @throws Error The preference service failed to restart correctly.
+   */
+  void resetPrefs();
+
+  /**
+   * Called to reset all preferences with user set values back to the
+   * application default values.
+   */
+  void resetUserPrefs();
+
+  /**
+   * Called to write current preferences state to a file.
+   *
+   * @param aFile The file to be written.
+   *
+   * @note
+   * If nullptr is passed in for the aFile parameter the preference data is
+   * written out to the current preferences file (usually prefs.js.)
+   *
+   * @throws Error File failed to write.
+   *
+   * @see readUserPrefs
+   * @see nsIFile
+   */
+  void savePrefFile(in nsIFile aFile);
+
+  /**
+   * Call to get a Preferences "Branch" which accesses user preference data.
+   * Using a Set method on this object will always create or set a user
+   * preference value. When using a Get method a user set value will be
+   * returned if one exists, otherwise a default value will be returned.
+   *
+   * @param aPrefRoot The preference "root" on which to base this "branch".
+   *                  For example, if the root "browser.startup." is used, the
+   *                  branch will be able to easily access the preferences
+   *                  "browser.startup.page", "browser.startup.homepage", or
+   *                  "browser.startup.homepage_override" by simply requesting
+   *                  "page", "homepage", or "homepage_override". nullptr or "" 
+   *                  may be used to access to the entire preference "tree".
+   *
+   * @return nsIPrefBranch The object representing the requested branch.
+   *
+   * @see getDefaultBranch
+   */
+  nsIPrefBranch getBranch(in string aPrefRoot);
+
+  /**
+   * Call to get a Preferences "Branch" which accesses only the default 
+   * preference data. Using a Set method on this object will always create or
+   * set a default preference value. When using a Get method a default value
+   * will always be returned.
+   *
+   * @param aPrefRoot The preference "root" on which to base this "branch".
+   *                  For example, if the root "browser.startup." is used, the
+   *                  branch will be able to easily access the preferences
+   *                  "browser.startup.page", "browser.startup.homepage", or
+   *                  "browser.startup.homepage_override" by simply requesting
+   *                  "page", "homepage", or "homepage_override". nullptr or "" 
+   *                  may be used to access to the entire preference "tree".
+   *
+   * @note
+   * Few consumers will want to create default branch objects. Many of the
+   * branch methods do nothing on a default branch because the operations only
+   * make sense when applied to user set preferences.
+   *
+   * @return nsIPrefBranch The object representing the requested default branch.
+   *
+   * @see getBranch
+   */
+  nsIPrefBranch getDefaultBranch(in string aPrefRoot);
+
+  /**
+   * The preference service is 'dirty' if there are changes to user preferences
+   * that have not been written to disk
+   */
+  readonly attribute boolean dirty;
+};
+
+%{C++
+
+#define NS_PREFSERVICE_CID                             \
+  { /* {1cd91b88-1dd2-11b2-92e1-ed22ed298000} */       \
+    0x91ca2441,                                        \
+    0x050f,                                            \
+    0x4f7c,                                            \
+    { 0x9d, 0xf8, 0x75, 0xb4, 0x0e, 0xa4, 0x01, 0x56 } \
+  }
+
+#define NS_PREFSERVICE_CONTRACTID "@mozilla.org/preferences-service;1"
+
+/**
+ * Notification sent before reading the default user preferences files.
+ */
+#define NS_PREFSERVICE_READ_TOPIC_ID "prefservice:before-read-userprefs"
+
+/**
+ * Notification sent when resetPrefs has been called, but before the actual
+ * reset process occurs.
+ */
+#define NS_PREFSERVICE_RESET_TOPIC_ID "prefservice:before-reset"
+
+/**
+ * Notification sent when after reading app-provided default
+ * preferences, but before user profile override defaults or extension
+ * defaults are loaded.
+ */
+#define NS_PREFSERVICE_APPDEFAULTS_TOPIC_ID "prefservice:after-app-defaults"
+
+%}
diff --git a/components/preferences/public/nsIRelativeFilePref.idl b/components/preferences/public/nsIRelativeFilePref.idl
new file mode 100644
index 000000000..4b86e3755
--- /dev/null
+++ b/components/preferences/public/nsIRelativeFilePref.idl
@@ -0,0 +1,69 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+interface nsIFile;
+
+/**
+ * The nsIRelativeFilePref interface is a wrapper for an nsIFile and
+ * and a directory service key. When used as a pref value, it stores a
+ * relative path to the file from the location pointed to by the directory
+ * service key. The path has the same syntax across all platforms.
+ *
+ * @see nsIPrefBranch::getComplexValue
+ * @see nsIPrefBranch::setComplexValue
+ * 
+ */
+
+[scriptable, uuid(2f977d4e-5485-11d4-87e2-0010a4e75ef2)]
+interface nsIRelativeFilePref : nsISupports
+{
+  /**
+   * file
+   *
+   * The file whose location is stored or retrieved.
+   */
+  attribute nsIFile file;
+
+  /**
+   * relativeToKey
+   *
+   * A directory service key for the directory
+   * from which the file path is relative.
+   */
+  attribute ACString relativeToKey;
+
+};
+
+%{C++
+
+#define NS_RELATIVEFILEPREF_CID                        \
+  { /* {2f977d4f-5485-11d4-87e2-0010a4e75ef2} */       \
+    0x2f977d4f,                                        \
+    0x5485,                                            \
+    0x11d4,                                            \
+    { 0x87, 0xe2, 0x00, 0x10, 0xa4, 0xe7, 0x5e, 0xf2 } \
+  }
+
+#define NS_RELATIVEFILEPREF_CONTRACTID "@mozilla.org/pref-relativefile;1"
+
+#include "nsComponentManagerUtils.h"
+
+inline nsresult
+NS_NewRelativeFilePref(nsIFile* aFile, const nsACString& relativeToKey, nsIRelativeFilePref** result)
+{
+    nsresult rv;
+    nsCOMPtr<nsIRelativeFilePref> local(do_CreateInstance(NS_RELATIVEFILEPREF_CONTRACTID, &rv));
+    if (NS_FAILED(rv)) return rv;
+    
+    (void)local->SetFile(aFile);
+    (void)local->SetRelativeToKey(relativeToKey);
+
+    *result = local;
+    NS_ADDREF(*result);
+    return NS_OK;
+}
+
+%}
diff --git a/components/preferences/src/Preferences.cpp b/components/preferences/src/Preferences.cpp
new file mode 100644
index 000000000..5f17125da
--- /dev/null
+++ b/components/preferences/src/Preferences.cpp
@@ -0,0 +1,1988 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/dom/ContentChild.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/UniquePtrExtensions.h"
+
+#include "nsXULAppAPI.h"
+
+#include "mozilla/Preferences.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsDataHashtable.h"
+#include "nsDirectoryServiceDefs.h"
+#include "nsICategoryManager.h"
+#include "nsCategoryManagerUtils.h"
+#include "nsNetUtil.h"
+#include "nsIFile.h"
+#include "nsIInputStream.h"
+#include "nsIObserverService.h"
+#include "nsIOutputStream.h"
+#include "nsISafeOutputStream.h"
+#include "nsISimpleEnumerator.h"
+#include "nsIStringEnumerator.h"
+#include "nsIZipReader.h"
+#include "nsPrefBranch.h"
+#include "nsXPIDLString.h"
+#include "nsCRT.h"
+#include "nsCOMArray.h"
+#include "nsXPCOMCID.h"
+#include "nsAutoPtr.h"
+#include "nsPrintfCString.h"
+
+#include "nsQuickSort.h"
+#include "PLDHashTable.h"
+
+#include "prefapi.h"
+#include "prefread.h"
+#include "prefapi_private_data.h"
+
+#include "mozilla/Omnijar.h"
+#include "nsZipArchive.h"
+
+#include "nsTArray.h"
+#include "nsRefPtrHashtable.h"
+#include "nsIMemoryReporter.h"
+#include "nsThreadUtils.h"
+
+#ifdef DEBUG
+#define ENSURE_MAIN_PROCESS(message, pref) do {                                \
+  if (MOZ_UNLIKELY(!XRE_IsParentProcess())) {        \
+    nsPrintfCString msg("ENSURE_MAIN_PROCESS failed. %s %s", message, pref);   \
+    NS_WARNING(msg.get());                                                     \
+    return NS_ERROR_NOT_AVAILABLE;                                             \
+  }                                                                            \
+} while (0);
+#else
+#define ENSURE_MAIN_PROCESS(message, pref)                                     \
+  if (MOZ_UNLIKELY(!XRE_IsParentProcess())) {        \
+    return NS_ERROR_NOT_AVAILABLE;                                             \
+  }
+#endif
+
+class PrefCallback;
+
+namespace mozilla {
+
+// Definitions
+#define INITIAL_PREF_FILES 10
+static NS_DEFINE_CID(kZipReaderCID, NS_ZIPREADER_CID);
+
+void
+Preferences::DirtyCallback()
+{
+  if (gHashTable && sPreferences && !sPreferences->mDirty) {
+    sPreferences->mDirty = true;
+  }
+}
+
+// Prototypes
+static nsresult openPrefFile(nsIFile* aFile);
+static nsresult pref_InitInitialObjects(void);
+static nsresult pref_LoadPrefsInDirList(const char *listId);
+static nsresult ReadExtensionPrefs(nsIFile *aFile);
+
+static const char kChannelPref[] = "app.update.channel";
+
+static const char kPrefFileHeader[] =
+  "# Mozilla User Preferences"
+  NS_LINEBREAK
+  NS_LINEBREAK
+  "/* Do not edit this file."
+  NS_LINEBREAK
+  " *"
+  NS_LINEBREAK
+  " * If you make changes to this file while the application is running,"
+  NS_LINEBREAK
+  " * the changes will be overwritten when the application exits."
+  NS_LINEBREAK
+  " *"
+  NS_LINEBREAK
+  " * To make a manual change to preferences, you can visit the URL about:config"
+  NS_LINEBREAK
+  " */"
+  NS_LINEBREAK
+  NS_LINEBREAK;
+
+Preferences* Preferences::sPreferences = nullptr;
+nsIPrefBranch* Preferences::sRootBranch = nullptr;
+nsIPrefBranch* Preferences::sDefaultRootBranch = nullptr;
+bool Preferences::sShutdown = false;
+
+class ValueObserverHashKey : public PLDHashEntryHdr {
+public:
+  typedef ValueObserverHashKey* KeyType;
+  typedef const ValueObserverHashKey* KeyTypePointer;
+
+  static const ValueObserverHashKey* KeyToPointer(ValueObserverHashKey *aKey)
+  {
+    return aKey;
+  }
+
+  static PLDHashNumber HashKey(const ValueObserverHashKey *aKey)
+  {
+    PLDHashNumber hash = HashString(aKey->mPrefName);
+    hash = AddToHash(hash, aKey->mMatchKind);
+    return AddToHash(hash, aKey->mCallback);
+  }
+
+  ValueObserverHashKey(const char *aPref, PrefChangedFunc aCallback, Preferences::MatchKind aMatchKind) :
+    mPrefName(aPref), mCallback(aCallback), mMatchKind(aMatchKind) { }
+
+  explicit ValueObserverHashKey(const ValueObserverHashKey *aOther) :
+    mPrefName(aOther->mPrefName),
+    mCallback(aOther->mCallback),
+    mMatchKind(aOther->mMatchKind)
+  { }
+
+  bool KeyEquals(const ValueObserverHashKey *aOther) const
+  {
+    return mCallback == aOther->mCallback &&
+           mPrefName == aOther->mPrefName &&
+           mMatchKind == aOther->mMatchKind;
+  }
+
+  ValueObserverHashKey *GetKey() const
+  {
+    return const_cast<ValueObserverHashKey*>(this);
+  }
+
+  enum { ALLOW_MEMMOVE = true };
+
+  nsCString mPrefName;
+  PrefChangedFunc mCallback;
+  Preferences::MatchKind mMatchKind;
+};
+
+class ValueObserver final : public nsIObserver,
+                            public ValueObserverHashKey
+{
+  ~ValueObserver() {
+    Preferences::RemoveObserver(this, mPrefName.get());
+  }
+
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  ValueObserver(const char *aPref, PrefChangedFunc aCallback, Preferences::MatchKind aMatchKind)
+    : ValueObserverHashKey(aPref, aCallback, aMatchKind) { }
+
+  void AppendClosure(void *aClosure) {
+    mClosures.AppendElement(aClosure);
+  }
+
+  void RemoveClosure(void *aClosure) {
+    mClosures.RemoveElement(aClosure);
+  }
+
+  bool HasNoClosures() {
+    return mClosures.Length() == 0;
+  }
+
+  nsTArray<void*> mClosures;
+};
+
+NS_IMPL_ISUPPORTS(ValueObserver, nsIObserver)
+
+NS_IMETHODIMP
+ValueObserver::Observe(nsISupports     *aSubject,
+                       const char      *aTopic,
+                       const char16_t *aData)
+{
+  NS_ASSERTION(!nsCRT::strcmp(aTopic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID),
+               "invalid topic");
+  NS_ConvertUTF16toUTF8 data(aData);
+  if (mMatchKind == Preferences::ExactMatch && !mPrefName.EqualsASCII(data.get())) {
+    return NS_OK;
+  }
+  for (uint32_t i = 0; i < mClosures.Length(); i++) {
+    mCallback(data.get(), mClosures.ElementAt(i));
+  }
+
+  return NS_OK;
+}
+
+struct CacheData {
+  void* cacheLocation;
+  union {
+    bool defaultValueBool;
+    int32_t defaultValueInt;
+    uint32_t defaultValueUint;
+    float defaultValueFloat;
+  };
+};
+
+static nsTArray<nsAutoPtr<CacheData> >* gCacheData = nullptr;
+static nsRefPtrHashtable<ValueObserverHashKey,
+                         ValueObserver>* gObserverTable = nullptr;
+
+#ifdef DEBUG
+static bool
+HaveExistingCacheFor(void* aPtr)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  if (gCacheData) {
+    for (size_t i = 0, count = gCacheData->Length(); i < count; ++i) {
+      if ((*gCacheData)[i]->cacheLocation == aPtr) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+static void
+AssertNotAlreadyCached(const char* aPrefType,
+                       const char* aPref,
+                       void* aPtr)
+{
+  if (HaveExistingCacheFor(aPtr)) {
+    fprintf_stderr(stderr,
+      "Attempt to add a %s pref cache for preference '%s' at address '%p'"
+      "was made. However, a pref was already cached at this address.\n",
+      aPrefType, aPref, aPtr);
+    MOZ_ASSERT(false, "Should not have an existing pref cache for this address");
+  }
+}
+#endif
+
+static void
+ReportToConsole(const char* aMessage, int aLine, bool aError)
+{
+  nsPrintfCString message("** Preference parsing %s (line %d) = %s **\n",
+                          (aError ? "error" : "warning"), aLine, aMessage);
+  nsPrefBranch::ReportToConsole(NS_ConvertUTF8toUTF16(message.get()));
+}
+
+// Although this is a member of Preferences, it measures sPreferences and
+// several other global structures.
+/* static */ int64_t
+Preferences::SizeOfIncludingThisAndOtherStuff(mozilla::MallocSizeOf aMallocSizeOf)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), 0);
+
+  size_t n = aMallocSizeOf(sPreferences);
+  if (gHashTable) {
+    // pref keys are allocated in a private arena, which we count elsewhere.
+    // pref stringvals are allocated out of the same private arena.
+    n += gHashTable->ShallowSizeOfIncludingThis(aMallocSizeOf);
+  }
+  if (gCacheData) {
+    n += gCacheData->ShallowSizeOfIncludingThis(aMallocSizeOf);
+    for (uint32_t i = 0, count = gCacheData->Length(); i < count; ++i) {
+      n += aMallocSizeOf((*gCacheData)[i]);
+    }
+  }
+  if (gObserverTable) {
+    n += gObserverTable->ShallowSizeOfIncludingThis(aMallocSizeOf);
+    for (auto iter = gObserverTable->Iter(); !iter.Done(); iter.Next()) {
+      n += iter.Key()->mPrefName.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+      n += iter.Data()->mClosures.ShallowSizeOfExcludingThis(aMallocSizeOf);
+    }
+  }
+  if (sRootBranch) {
+    n += reinterpret_cast<nsPrefBranch*>(sRootBranch)->SizeOfIncludingThis(aMallocSizeOf);
+  }
+  if (sDefaultRootBranch) {
+    n += reinterpret_cast<nsPrefBranch*>(sDefaultRootBranch)->SizeOfIncludingThis(aMallocSizeOf);
+  }
+  n += pref_SizeOfPrivateData(aMallocSizeOf);
+  return n;
+}
+
+class PreferenceServiceReporter final : public nsIMemoryReporter
+{
+  ~PreferenceServiceReporter() {}
+
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIMEMORYREPORTER
+
+protected:
+  static const uint32_t kSuspectReferentCount = 1000;
+};
+
+NS_IMPL_ISUPPORTS(PreferenceServiceReporter, nsIMemoryReporter)
+
+MOZ_DEFINE_MALLOC_SIZE_OF(PreferenceServiceMallocSizeOf)
+
+NS_IMETHODIMP
+PreferenceServiceReporter::CollectReports(
+  nsIHandleReportCallback* aHandleReport, nsISupports* aData, bool aAnonymize)
+{
+  MOZ_COLLECT_REPORT(
+    "explicit/preferences", KIND_HEAP, UNITS_BYTES,
+    Preferences::SizeOfIncludingThisAndOtherStuff(PreferenceServiceMallocSizeOf),
+    "Memory used by the preferences system.");
+
+  nsPrefBranch* rootBranch =
+    static_cast<nsPrefBranch*>(Preferences::GetRootBranch());
+  if (!rootBranch) {
+    return NS_OK;
+  }
+
+  size_t numStrong = 0;
+  size_t numWeakAlive = 0;
+  size_t numWeakDead = 0;
+  nsTArray<nsCString> suspectPreferences;
+  // Count of the number of referents for each preference.
+  nsDataHashtable<nsCStringHashKey, uint32_t> prefCounter;
+
+  for (auto iter = rootBranch->mObservers.Iter(); !iter.Done(); iter.Next()) {
+    nsAutoPtr<PrefCallback>& callback = iter.Data();
+    nsPrefBranch* prefBranch = callback->GetPrefBranch();
+    const char* pref = prefBranch->getPrefName(callback->GetDomain().get());
+
+    if (callback->IsWeak()) {
+      nsCOMPtr<nsIObserver> callbackRef = do_QueryReferent(callback->mWeakRef);
+      if (callbackRef) {
+        numWeakAlive++;
+      } else {
+        numWeakDead++;
+      }
+    } else {
+      numStrong++;
+    }
+
+    nsDependentCString prefString(pref);
+    uint32_t oldCount = 0;
+    prefCounter.Get(prefString, &oldCount);
+    uint32_t currentCount = oldCount + 1;
+    prefCounter.Put(prefString, currentCount);
+
+    // Keep track of preferences that have a suspiciously large number of
+    // referents (a symptom of a leak).
+    if (currentCount == kSuspectReferentCount) {
+      suspectPreferences.AppendElement(prefString);
+    }
+  }
+
+  for (uint32_t i = 0; i < suspectPreferences.Length(); i++) {
+    nsCString& suspect = suspectPreferences[i];
+    uint32_t totalReferentCount = 0;
+    prefCounter.Get(suspect, &totalReferentCount);
+
+    nsPrintfCString suspectPath("preference-service-suspect/"
+                                "referent(pref=%s)", suspect.get());
+
+    aHandleReport->Callback(
+      /* process = */ EmptyCString(),
+      suspectPath, KIND_OTHER, UNITS_COUNT, totalReferentCount,
+      NS_LITERAL_CSTRING(
+        "A preference with a suspiciously large number referents (symptom of a "
+        "leak)."),
+      aData);
+  }
+
+  MOZ_COLLECT_REPORT(
+    "preference-service/referent/strong", KIND_OTHER, UNITS_COUNT,
+    numStrong,
+    "The number of strong referents held by the preference service.");
+
+  MOZ_COLLECT_REPORT(
+    "preference-service/referent/weak/alive", KIND_OTHER, UNITS_COUNT,
+    numWeakAlive,
+    "The number of weak referents held by the preference service that are "
+    "still alive.");
+
+  MOZ_COLLECT_REPORT(
+    "preference-service/referent/weak/dead", KIND_OTHER, UNITS_COUNT,
+    numWeakDead,
+    "The number of weak referents held by the preference service that are "
+    "dead.");
+
+  return NS_OK;
+}
+
+namespace {
+class AddPreferencesMemoryReporterRunnable : public Runnable
+{
+  NS_IMETHOD Run() override
+  {
+    return RegisterStrongMemoryReporter(new PreferenceServiceReporter());
+  }
+};
+} // namespace
+
+// static
+Preferences*
+Preferences::GetInstanceForService()
+{
+  if (sPreferences) {
+    NS_ADDREF(sPreferences);
+    return sPreferences;
+  }
+
+  NS_ENSURE_TRUE(!sShutdown, nullptr);
+
+  sRootBranch = new nsPrefBranch("", false);
+  NS_ADDREF(sRootBranch);
+  sDefaultRootBranch = new nsPrefBranch("", true);
+  NS_ADDREF(sDefaultRootBranch);
+
+  sPreferences = new Preferences();
+  NS_ADDREF(sPreferences);
+
+  if (NS_FAILED(sPreferences->Init())) {
+    // The singleton instance will delete sRootBranch and sDefaultRootBranch.
+    NS_RELEASE(sPreferences);
+    return nullptr;
+  }
+
+  gCacheData = new nsTArray<nsAutoPtr<CacheData> >();
+
+  gObserverTable = new nsRefPtrHashtable<ValueObserverHashKey, ValueObserver>();
+
+  // Preferences::GetInstanceForService() can be called from GetService(), and
+  // RegisterStrongMemoryReporter calls GetService(nsIMemoryReporter).  To
+  // avoid a potential recursive GetService() call, we can't register the
+  // memory reporter here; instead, do it off a runnable.
+  RefPtr<AddPreferencesMemoryReporterRunnable> runnable =
+    new AddPreferencesMemoryReporterRunnable();
+  NS_DispatchToMainThread(runnable);
+
+  NS_ADDREF(sPreferences);
+  return sPreferences;
+}
+
+// static
+bool
+Preferences::IsServiceAvailable()
+{
+  return !!sPreferences;
+}
+
+// static
+bool
+Preferences::InitStaticMembers()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!sShutdown && !sPreferences) {
+    nsCOMPtr<nsIPrefService> prefService =
+      do_GetService(NS_PREFSERVICE_CONTRACTID);
+  }
+
+  return sPreferences != nullptr;
+}
+
+// static
+void
+Preferences::Shutdown()
+{
+  if (!sShutdown) {
+    sShutdown = true; // Don't create the singleton instance after here.
+
+    // Don't set sPreferences to nullptr here.  The instance may be grabbed by
+    // other modules.  The utility methods of Preferences should be available
+    // until the singleton instance actually released.
+    if (sPreferences) {
+      sPreferences->Release();
+    }
+  }
+}
+
+//-----------------------------------------------------------------------------
+
+/*
+ * Constructor/Destructor
+ */
+
+Preferences::Preferences()
+  : mDirty(false)
+{
+}
+
+Preferences::~Preferences()
+{
+  NS_ASSERTION(sPreferences == this, "Isn't this the singleton instance?");
+
+  delete gObserverTable;
+  gObserverTable = nullptr;
+
+  delete gCacheData;
+  gCacheData = nullptr;
+
+  NS_RELEASE(sRootBranch);
+  NS_RELEASE(sDefaultRootBranch);
+
+  sPreferences = nullptr;
+
+  PREF_Cleanup();
+}
+
+
+/*
+ * nsISupports Implementation
+ */
+
+NS_IMPL_ADDREF(Preferences)
+NS_IMPL_RELEASE(Preferences)
+
+NS_INTERFACE_MAP_BEGIN(Preferences)
+    NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIPrefService)
+    NS_INTERFACE_MAP_ENTRY(nsIPrefService)
+    NS_INTERFACE_MAP_ENTRY(nsIObserver)
+    NS_INTERFACE_MAP_ENTRY(nsIPrefBranch)
+    NS_INTERFACE_MAP_ENTRY(nsIPrefBranch2)
+    NS_INTERFACE_MAP_ENTRY(nsIPrefBranchInternal)
+    NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+NS_INTERFACE_MAP_END
+
+
+/*
+ * nsIPrefService Implementation
+ */
+
+nsresult
+Preferences::Init()
+{
+  nsresult rv;
+
+  PREF_SetDirtyCallback(&DirtyCallback);
+  PREF_Init();
+
+  rv = pref_InitInitialObjects();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  using mozilla::dom::ContentChild;
+  if (XRE_IsContentProcess()) {
+    InfallibleTArray<PrefSetting> prefs;
+    ContentChild::GetSingleton()->SendReadPrefsArray(&prefs);
+
+    // Store the array
+    for (uint32_t i = 0; i < prefs.Length(); ++i) {
+      pref_SetPref(prefs[i]);
+    }
+    return NS_OK;
+  }
+
+  nsXPIDLCString lockFileName;
+  /*
+   * The following is a small hack which will allow us to only load the library
+   * which supports the netscape.cfg file if the preference is defined. We
+   * test for the existence of the pref, set in the all.js (mozilla) or
+   * all-ns.js (netscape 6), and if it exists we startup the pref config
+   * category which will do the rest.
+   */
+
+  rv = PREF_CopyCharPref("general.config.filename", getter_Copies(lockFileName), false);
+  if (NS_SUCCEEDED(rv))
+    NS_CreateServicesFromCategory("pref-config-startup",
+                                  static_cast<nsISupports *>(static_cast<void *>(this)),
+                                  "pref-config-startup");    
+
+  nsCOMPtr<nsIObserverService> observerService =
+    mozilla::services::GetObserverService();
+  if (!observerService)
+    return NS_ERROR_FAILURE;
+
+  rv = observerService->AddObserver(this, "profile-before-change", true);
+
+  observerService->AddObserver(this, "load-extension-defaults", true);
+  observerService->AddObserver(this, "suspend_process_notification", true);
+
+  return(rv);
+}
+
+// static
+nsresult
+Preferences::ResetAndReadUserPrefs()
+{
+  sPreferences->ResetUserPrefs();
+  return sPreferences->ReadUserPrefs(nullptr);
+}
+
+NS_IMETHODIMP
+Preferences::Observe(nsISupports *aSubject, const char *aTopic,
+                     const char16_t *someData)
+{
+  if (XRE_IsContentProcess())
+    return NS_ERROR_NOT_AVAILABLE;
+
+  nsresult rv = NS_OK;
+
+  if (!nsCRT::strcmp(aTopic, "profile-before-change")) {
+    rv = SavePrefFile(nullptr);
+  } else if (!strcmp(aTopic, "load-extension-defaults")) {
+    pref_LoadPrefsInDirList(NS_EXT_PREFS_DEFAULTS_DIR_LIST);
+  } else if (!nsCRT::strcmp(aTopic, "reload-default-prefs")) {
+    // Reload the default prefs from file.
+    pref_InitInitialObjects();
+  } else if (!nsCRT::strcmp(aTopic, "suspend_process_notification")) {
+    // Our process is being suspended. The OS may wake our process later,
+    // or it may kill the process. In case our process is going to be killed
+    // from the suspended state, we save preferences before suspending.
+    rv = SavePrefFile(nullptr);
+  }
+  return rv;
+}
+
+
+NS_IMETHODIMP
+Preferences::ReadUserPrefs(nsIFile *aFile)
+{
+  if (XRE_IsContentProcess()) {
+    NS_ERROR("cannot load prefs from content process");
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  nsresult rv;
+
+  if (nullptr == aFile) {
+    rv = UseDefaultPrefFile();
+    // A user pref file is optional.
+    // Ignore all errors related to it, so we retain 'rv' value :-|
+    (void) UseUserPrefFile();
+
+    NotifyServiceObservers(NS_PREFSERVICE_READ_TOPIC_ID);
+  } else {
+    rv = ReadAndOwnUserPrefFile(aFile);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+Preferences::ResetPrefs()
+{
+  if (XRE_IsContentProcess()) {
+    NS_ERROR("cannot reset prefs from content process");
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  NotifyServiceObservers(NS_PREFSERVICE_RESET_TOPIC_ID);
+  PREF_CleanupPrefs();
+
+  PREF_Init();
+
+  return pref_InitInitialObjects();
+}
+
+NS_IMETHODIMP
+Preferences::ResetUserPrefs()
+{
+  if (XRE_IsContentProcess()) {
+    NS_ERROR("cannot reset user prefs from content process");
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  PREF_ClearAllUserPrefs();
+  return NS_OK;    
+}
+
+NS_IMETHODIMP
+Preferences::SavePrefFile(nsIFile *aFile)
+{
+  if (XRE_IsContentProcess()) {
+    NS_ERROR("cannot save pref file from content process");
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  return SavePrefFileInternal(aFile);
+}
+
+static nsresult
+ReadExtensionPrefs(nsIFile *aFile)
+{
+  nsresult rv;
+  nsCOMPtr<nsIZipReader> reader = do_CreateInstance(kZipReaderCID, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = reader->Open(aFile);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIUTF8StringEnumerator> files;
+  rv = reader->FindEntries(nsDependentCString("defaults/preferences/*.(J|j)(S|s)$"),
+                           getter_AddRefs(files));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  char buffer[4096];
+
+  bool more;
+  while (NS_SUCCEEDED(rv = files->HasMore(&more)) && more) {
+    nsAutoCString entry;
+    rv = files->GetNext(entry);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<nsIInputStream> stream;
+    rv = reader->GetInputStream(entry, getter_AddRefs(stream));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    uint64_t avail;
+    uint32_t read;
+
+    PrefParseState ps;
+    PREF_InitParseState(&ps, PREF_ReaderCallback, ReportToConsole, nullptr);
+    while (NS_SUCCEEDED(rv = stream->Available(&avail)) && avail) {
+      rv = stream->Read(buffer, 4096, &read);
+      if (NS_FAILED(rv)) {
+        NS_WARNING("Pref stream read failed");
+        break;
+      }
+
+      PREF_ParseBuf(&ps, buffer, read);
+    }
+    PREF_FinalizeParseState(&ps);
+  }
+  return rv;
+}
+
+void
+Preferences::SetPreference(const PrefSetting& aPref)
+{
+  pref_SetPref(aPref);
+}
+
+void
+Preferences::GetPreference(PrefSetting* aPref)
+{
+  PrefHashEntry *entry = pref_HashTableLookup(aPref->name().get());
+  if (!entry)
+    return;
+
+  if (pref_EntryHasAdvisablySizedValues(entry)) {
+    pref_GetPrefFromEntry(entry, aPref);
+  }
+}
+
+void
+Preferences::GetPreferences(InfallibleTArray<PrefSetting>* aPrefs)
+{
+  aPrefs->SetCapacity(gHashTable->Capacity());
+  for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
+    auto entry = static_cast<PrefHashEntry*>(iter.Get());
+
+    if (!pref_EntryHasAdvisablySizedValues(entry)) {
+      continue;
+    }
+
+    dom::PrefSetting *pref = aPrefs->AppendElement();
+    pref_GetPrefFromEntry(entry, pref);
+  }
+}
+
+NS_IMETHODIMP
+Preferences::GetBranch(const char *aPrefRoot, nsIPrefBranch **_retval)
+{
+  nsresult rv;
+
+  if ((nullptr != aPrefRoot) && (*aPrefRoot != '\0')) {
+    // TODO: - cache this stuff and allow consumers to share branches (hold weak references I think)
+    RefPtr<nsPrefBranch> prefBranch = new nsPrefBranch(aPrefRoot, false);
+    prefBranch.forget(_retval);
+    rv = NS_OK;
+  } else {
+    // special case caching the default root
+    nsCOMPtr<nsIPrefBranch> root(sRootBranch);
+    root.forget(_retval);
+    rv = NS_OK;
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+Preferences::GetDefaultBranch(const char *aPrefRoot, nsIPrefBranch **_retval)
+{
+  if (!aPrefRoot || !aPrefRoot[0]) {
+    nsCOMPtr<nsIPrefBranch> root(sDefaultRootBranch);
+    root.forget(_retval);
+    return NS_OK;
+  }
+
+  // TODO: - cache this stuff and allow consumers to share branches (hold weak references I think)
+  RefPtr<nsPrefBranch> prefBranch = new nsPrefBranch(aPrefRoot, true);
+  if (!prefBranch)
+    return NS_ERROR_OUT_OF_MEMORY;
+
+  prefBranch.forget(_retval);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+Preferences::GetDirty(bool *_retval) {
+  *_retval = mDirty;
+  return NS_OK;
+}
+
+nsresult
+Preferences::NotifyServiceObservers(const char *aTopic)
+{
+  nsCOMPtr<nsIObserverService> observerService = 
+    mozilla::services::GetObserverService();  
+  if (!observerService)
+    return NS_ERROR_FAILURE;
+
+  nsISupports *subject = (nsISupports *)((nsIPrefService *)this);
+  observerService->NotifyObservers(subject, aTopic, nullptr);
+  
+  return NS_OK;
+}
+
+nsresult
+Preferences::UseDefaultPrefFile()
+{
+  nsCOMPtr<nsIFile> aFile;
+  nsresult rv = NS_GetSpecialDirectory(NS_APP_PREFS_50_FILE, getter_AddRefs(aFile));
+
+  if (NS_SUCCEEDED(rv)) {
+    rv = ReadAndOwnUserPrefFile(aFile);
+    // Most likely cause of failure here is that the file didn't
+    // exist, so save a new one. mUserPrefReadFailed will be
+    // used to catch an error in actually reading the file.
+    if (NS_FAILED(rv)) {
+      if (NS_FAILED(SavePrefFileInternal(aFile)))
+        NS_ERROR("Failed to save new shared pref file");
+      else
+        rv = NS_OK;
+    }
+  }
+  
+  return rv;
+}
+
+nsresult
+Preferences::UseUserPrefFile()
+{
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIFile> aFile;
+  nsDependentCString prefsDirProp(NS_APP_PREFS_50_DIR);
+
+  rv = NS_GetSpecialDirectory(prefsDirProp.get(), getter_AddRefs(aFile));
+  if (NS_SUCCEEDED(rv) && aFile) {
+    rv = aFile->AppendNative(NS_LITERAL_CSTRING("user.js"));
+    if (NS_SUCCEEDED(rv)) {
+      bool exists = false;
+      aFile->Exists(&exists);
+      if (exists) {
+        rv = openPrefFile(aFile);
+      } else {
+        rv = NS_ERROR_FILE_NOT_FOUND;
+      }
+    }
+  }
+  return rv;
+}
+
+nsresult
+Preferences::MakeBackupPrefFile(nsIFile *aFile)
+{
+  // Example: this copies "prefs.js" to "Invalidprefs.js" in the same directory.
+  // "Invalidprefs.js" is removed if it exists, prior to making the copy.
+  nsAutoString newFilename;
+  nsresult rv = aFile->GetLeafName(newFilename);
+  NS_ENSURE_SUCCESS(rv, rv);
+  newFilename.Insert(NS_LITERAL_STRING("Invalid"), 0);
+  nsCOMPtr<nsIFile> newFile;
+  rv = aFile->GetParent(getter_AddRefs(newFile));
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = newFile->Append(newFilename);
+  NS_ENSURE_SUCCESS(rv, rv);
+  bool exists = false;
+  newFile->Exists(&exists);
+  if (exists) {
+    rv = newFile->Remove(false);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  rv = aFile->CopyTo(nullptr, newFilename);
+  NS_ENSURE_SUCCESS(rv, rv);
+  return rv;
+}
+
+nsresult
+Preferences::ReadAndOwnUserPrefFile(nsIFile *aFile)
+{
+  NS_ENSURE_ARG(aFile);
+  
+  if (mCurrentFile == aFile)
+    return NS_OK;
+  mCurrentFile = aFile;
+
+  nsresult rv = NS_OK;
+  bool exists = false;
+  mCurrentFile->Exists(&exists);
+  if (exists) {
+    rv = openPrefFile(mCurrentFile);
+    if (NS_FAILED(rv)) {
+      // Save a backup copy of the current (invalid) prefs file, since all prefs
+      // from the error line to the end of the file will be lost (bug 361102).
+      // TODO we should notify the user about it (bug 523725).
+      MakeBackupPrefFile(mCurrentFile);
+    }
+  } else {
+    rv = NS_ERROR_FILE_NOT_FOUND;
+  }
+
+  return rv;
+}
+
+nsresult
+Preferences::SavePrefFileInternal(nsIFile *aFile)
+{
+  if (nullptr == aFile) {
+    // the mDirty flag tells us if we should write to mCurrentFile
+    // we only check this flag when the caller wants to write to the default
+    if (!mDirty) {
+      return NS_OK;
+    }
+
+    // It's possible that we never got a prefs file.
+    nsresult rv = NS_OK;
+    if (mCurrentFile)
+      rv = WritePrefFile(mCurrentFile);
+
+    return rv;
+  } else {
+    return WritePrefFile(aFile);
+  }
+}
+
+nsresult
+Preferences::WritePrefFile(nsIFile* aFile)
+{
+  nsCOMPtr<nsIOutputStream> outStreamSink;
+  nsCOMPtr<nsIOutputStream> outStream;
+  uint32_t                  writeAmount;
+  nsresult                  rv;
+
+  if (!gHashTable)
+    return NS_ERROR_NOT_INITIALIZED;
+
+  // execute a "safe" save by saving through a tempfile
+  rv = NS_NewSafeLocalFileOutputStream(getter_AddRefs(outStreamSink),
+                                       aFile,
+                                       -1,
+                                       0600);
+  if (NS_FAILED(rv)) 
+      return rv;
+  rv = NS_NewBufferedOutputStream(getter_AddRefs(outStream), outStreamSink, 4096);
+  if (NS_FAILED(rv)) 
+      return rv;  
+
+  // get the lines that we're supposed to be writing to the file
+  uint32_t prefCount;
+  UniquePtr<char*[]> valueArray = pref_savePrefs(gHashTable, &prefCount);
+
+  /* Sort the preferences to make a readable file on disk */
+  NS_QuickSort(valueArray.get(), prefCount, sizeof(char *),
+               pref_CompareStrings, nullptr);
+
+  // write out the file header
+  outStream->Write(kPrefFileHeader, sizeof(kPrefFileHeader) - 1, &writeAmount);
+
+  for (uint32_t valueIdx = 0; valueIdx < prefCount; valueIdx++) {
+    char*& pref = valueArray[valueIdx];
+    MOZ_ASSERT(pref);
+    outStream->Write(pref, strlen(pref), &writeAmount);
+    outStream->Write(NS_LINEBREAK, NS_LINEBREAK_LEN, &writeAmount);
+    free(pref);
+    pref = nullptr;
+  }
+
+  // tell the safe output stream to overwrite the real prefs file
+  // (it'll abort if there were any errors during writing)
+  nsCOMPtr<nsISafeOutputStream> safeStream = do_QueryInterface(outStream);
+  NS_ASSERTION(safeStream, "expected a safe output stream!");
+  if (safeStream) {
+    rv = safeStream->Finish();
+    if (NS_FAILED(rv)) {
+      NS_WARNING("failed to save prefs file! possible data loss");
+      return rv;
+    }
+  }
+
+  mDirty = false;
+  return NS_OK;
+}
+
+static nsresult openPrefFile(nsIFile* aFile)
+{
+  nsCOMPtr<nsIInputStream> inStr;
+
+  nsresult rv = NS_NewLocalFileInputStream(getter_AddRefs(inStr), aFile);
+  if (NS_FAILED(rv)) 
+    return rv;        
+
+  int64_t fileSize64;
+  rv = aFile->GetFileSize(&fileSize64);
+  if (NS_FAILED(rv))
+    return rv;
+  NS_ENSURE_TRUE(fileSize64 <= UINT32_MAX, NS_ERROR_FILE_TOO_BIG);
+
+  uint32_t fileSize = (uint32_t)fileSize64;
+  auto fileBuffer = MakeUniqueFallible<char[]>(fileSize);
+  if (fileBuffer == nullptr)
+    return NS_ERROR_OUT_OF_MEMORY;
+
+  PrefParseState ps;
+  PREF_InitParseState(&ps, PREF_ReaderCallback, ReportToConsole, nullptr);
+
+  // Read is not guaranteed to return a buf the size of fileSize,
+  // but usually will.
+  nsresult rv2 = NS_OK;
+  uint32_t offset = 0;
+  for (;;) {
+    uint32_t amtRead = 0;
+    rv = inStr->Read(fileBuffer.get(), fileSize, &amtRead);
+    if (NS_FAILED(rv) || amtRead == 0)
+      break;
+    if (!PREF_ParseBuf(&ps, fileBuffer.get(), amtRead))
+      rv2 = NS_ERROR_FILE_CORRUPTED;
+    offset += amtRead;
+    if (offset == fileSize) {
+      break;
+    }
+  }
+
+  PREF_FinalizeParseState(&ps);
+
+  return NS_FAILED(rv) ? rv : rv2;
+}
+
+/*
+ * some stuff that gets called from Pref_Init()
+ */
+
+static int
+pref_CompareFileNames(nsIFile* aFile1, nsIFile* aFile2, void* /*unused*/)
+{
+  nsAutoCString filename1, filename2;
+  aFile1->GetNativeLeafName(filename1);
+  aFile2->GetNativeLeafName(filename2);
+
+  return Compare(filename2, filename1);
+}
+
+/**
+ * Load default pref files from a directory. The files in the
+ * directory are sorted reverse-alphabetically; a set of "special file
+ * names" may be specified which are loaded after all the others.
+ */
+static nsresult
+pref_LoadPrefsInDir(nsIFile* aDir, char const *const *aSpecialFiles, uint32_t aSpecialFilesCount)
+{
+  nsresult rv, rv2;
+  bool hasMoreElements;
+
+  nsCOMPtr<nsISimpleEnumerator> dirIterator;
+
+  // this may fail in some normal cases, such as embedders who do not use a GRE
+  rv = aDir->GetDirectoryEntries(getter_AddRefs(dirIterator));
+  if (NS_FAILED(rv)) {
+    // If the directory doesn't exist, then we have no reason to complain.  We
+    // loaded everything (and nothing) successfully.
+    if (rv == NS_ERROR_FILE_NOT_FOUND || rv == NS_ERROR_FILE_TARGET_DOES_NOT_EXIST)
+      rv = NS_OK;
+    return rv;
+  }
+
+  rv = dirIterator->HasMoreElements(&hasMoreElements);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMArray<nsIFile> prefFiles(INITIAL_PREF_FILES);
+  nsCOMArray<nsIFile> specialFiles(aSpecialFilesCount);
+  nsCOMPtr<nsIFile> prefFile;
+
+  while (hasMoreElements && NS_SUCCEEDED(rv)) {
+    nsAutoCString leafName;
+
+    nsCOMPtr<nsISupports> supports;
+    rv = dirIterator->GetNext(getter_AddRefs(supports));
+    prefFile = do_QueryInterface(supports);
+    if (NS_FAILED(rv)) {
+      break;
+    }
+
+    prefFile->GetNativeLeafName(leafName);
+    NS_ASSERTION(!leafName.IsEmpty(), "Failure in default prefs: directory enumerator returned empty file?");
+
+    // Skip non-js files
+    if (StringEndsWith(leafName, NS_LITERAL_CSTRING(".js"),
+                       nsCaseInsensitiveCStringComparator())) {
+      bool shouldParse = true;
+      // separate out special files
+      for (uint32_t i = 0; i < aSpecialFilesCount; ++i) {
+        if (leafName.Equals(nsDependentCString(aSpecialFiles[i]))) {
+          shouldParse = false;
+          // special files should be process in order; we put them into
+          // the array by index; this can make the array sparse
+          specialFiles.ReplaceObjectAt(prefFile, i);
+        }
+      }
+
+      if (shouldParse) {
+        prefFiles.AppendObject(prefFile);
+      }
+    }
+
+    rv = dirIterator->HasMoreElements(&hasMoreElements);
+  }
+
+  if (prefFiles.Count() + specialFiles.Count() == 0) {
+    NS_WARNING("No default pref files found.");
+    if (NS_SUCCEEDED(rv)) {
+      rv = NS_SUCCESS_FILE_DIRECTORY_EMPTY;
+    }
+    return rv;
+  }
+
+  prefFiles.Sort(pref_CompareFileNames, nullptr);
+  
+  uint32_t arrayCount = prefFiles.Count();
+  uint32_t i;
+  for (i = 0; i < arrayCount; ++i) {
+    rv2 = openPrefFile(prefFiles[i]);
+    if (NS_FAILED(rv2)) {
+      NS_ERROR("Default pref file not parsed successfully.");
+      rv = rv2;
+    }
+  }
+
+  arrayCount = specialFiles.Count();
+  for (i = 0; i < arrayCount; ++i) {
+    // this may be a sparse array; test before parsing
+    nsIFile* file = specialFiles[i];
+    if (file) {
+      rv2 = openPrefFile(file);
+      if (NS_FAILED(rv2)) {
+        NS_ERROR("Special default pref file not parsed successfully.");
+        rv = rv2;
+      }
+    }
+  }
+
+  return rv;
+}
+
+static nsresult pref_LoadPrefsInDirList(const char *listId)
+{
+  nsresult rv;
+  nsCOMPtr<nsIProperties> dirSvc(do_GetService(NS_DIRECTORY_SERVICE_CONTRACTID, &rv));
+  if (NS_FAILED(rv))
+    return rv;
+
+  nsCOMPtr<nsISimpleEnumerator> list;
+  dirSvc->Get(listId,
+              NS_GET_IID(nsISimpleEnumerator),
+              getter_AddRefs(list));
+  if (!list)
+    return NS_OK;
+
+  bool hasMore;
+  while (NS_SUCCEEDED(list->HasMoreElements(&hasMore)) && hasMore) {
+    nsCOMPtr<nsISupports> elem;
+    list->GetNext(getter_AddRefs(elem));
+    if (!elem)
+      continue;
+
+    nsCOMPtr<nsIFile> path = do_QueryInterface(elem);
+    if (!path)
+      continue;
+
+    nsAutoCString leaf;
+    path->GetNativeLeafName(leaf);
+
+    // Do we care if a file provided by this process fails to load?
+    if (Substring(leaf, leaf.Length() - 4).EqualsLiteral(".xpi"))
+      ReadExtensionPrefs(path);
+    else
+      pref_LoadPrefsInDir(path, nullptr, 0);
+  }
+  return NS_OK;
+}
+
+static nsresult pref_ReadPrefFromJar(nsZipArchive* jarReader, const char *name)
+{
+  nsZipItemPtr<char> manifest(jarReader, name, true);
+  NS_ENSURE_TRUE(manifest.Buffer(), NS_ERROR_NOT_AVAILABLE);
+
+  PrefParseState ps;
+  PREF_InitParseState(&ps, PREF_ReaderCallback, ReportToConsole, nullptr);
+  PREF_ParseBuf(&ps, manifest, manifest.Length());
+  PREF_FinalizeParseState(&ps);
+
+  return NS_OK;
+}
+
+//----------------------------------------------------------------------------------------
+// Initialize default preference JavaScript buffers from
+// appropriate TEXT resources
+//----------------------------------------------------------------------------------------
+static nsresult pref_InitInitialObjects()
+{
+  nsresult rv;
+
+  // In omni.jar case, we load the following prefs:
+  // - jar:$gre/omni.jar!/goanna.js
+  // - jar:$gre/omni.jar!/defaults/pref/*.js
+  // In non omni.jar case, we load:
+  // - $gre/goanna.js
+  //
+  // In both cases, we also load:
+  // - $gre/defaults/pref/*.js
+  // This is kept for bug 591866 (channel-prefs.js should not be in omni.jar)
+  // on $app == $gre case ; we load all files instead of channel-prefs.js only
+  // to have the same behaviour as $app != $gre, where this is required as
+  // a supported location for GRE preferences.
+  //
+  // When $app != $gre, we additionally load, in omni.jar case:
+  // - jar:$app/omni.jar!/defaults/preferences/*.js
+  // - $app/defaults/preferences/*.js
+  // and in non omni.jar case:
+  // - $app/defaults/preferences/*.js
+  // When $app == $gre, we additionally load, in omni.jar case:
+  // - jar:$gre/omni.jar!/defaults/preferences/*.js
+  // Thus, in omni.jar case, we always load app-specific default preferences
+  // from omni.jar, whether or not $app == $gre.
+
+  nsZipFind *findPtr;
+  nsAutoPtr<nsZipFind> find;
+  nsTArray<nsCString> prefEntries;
+  const char *entryName;
+  uint16_t entryNameLen;
+
+  RefPtr<nsZipArchive> jarReader = mozilla::Omnijar::GetReader(mozilla::Omnijar::GRE);
+  if (jarReader) {
+    // Load jar:$gre/omni.jar!/goanna.js
+    rv = pref_ReadPrefFromJar(jarReader, "goanna.js");
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // Load jar:$gre/omni.jar!/defaults/pref/*.js
+    rv = jarReader->FindInit("defaults/pref/*.js$", &findPtr);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    find = findPtr;
+    while (NS_SUCCEEDED(find->FindNext(&entryName, &entryNameLen))) {
+      prefEntries.AppendElement(Substring(entryName, entryNameLen));
+    }
+
+    prefEntries.Sort();
+    for (uint32_t i = prefEntries.Length(); i--; ) {
+      rv = pref_ReadPrefFromJar(jarReader, prefEntries[i].get());
+      if (NS_FAILED(rv))
+        NS_WARNING("Error parsing preferences.");
+    }
+  } else {
+    // Load $gre/goanna.js
+    nsCOMPtr<nsIFile> greprefsFile;
+    rv = NS_GetSpecialDirectory(NS_GRE_DIR, getter_AddRefs(greprefsFile));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = greprefsFile->AppendNative(NS_LITERAL_CSTRING("goanna.js"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = openPrefFile(greprefsFile);
+    if (NS_FAILED(rv))
+      NS_WARNING("Error parsing GRE default preferences. Is this an old-style embedding app?");
+  }
+
+  // Load $gre/defaults/pref/*.js
+  nsCOMPtr<nsIFile> defaultPrefDir;
+
+  rv = NS_GetSpecialDirectory(NS_APP_PREF_DEFAULTS_50_DIR, getter_AddRefs(defaultPrefDir));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  /* these pref file names should not be used: we process them after all other application pref files for backwards compatibility */
+  static const char* specialFiles[] = {
+#if defined(XP_WIN)
+    "winpref.js"
+#elif defined(XP_UNIX)
+    "unix.js"
+#endif
+  };
+
+  rv = pref_LoadPrefsInDir(defaultPrefDir, specialFiles, ArrayLength(specialFiles));
+  if (NS_FAILED(rv))
+    NS_WARNING("Error parsing application default preferences.");
+
+  // Load jar:$app/omni.jar!/defaults/preferences/*.js
+  // or jar:$gre/omni.jar!/defaults/preferences/*.js.
+  RefPtr<nsZipArchive> appJarReader = mozilla::Omnijar::GetReader(mozilla::Omnijar::APP);
+  // GetReader(mozilla::Omnijar::APP) returns null when $app == $gre, in which
+  // case we look for app-specific default preferences in $gre.
+  if (!appJarReader)
+    appJarReader = mozilla::Omnijar::GetReader(mozilla::Omnijar::GRE);
+  if (appJarReader) {
+    rv = appJarReader->FindInit("defaults/preferences/*.js$", &findPtr);
+    NS_ENSURE_SUCCESS(rv, rv);
+    find = findPtr;
+    prefEntries.Clear();
+    while (NS_SUCCEEDED(find->FindNext(&entryName, &entryNameLen))) {
+      prefEntries.AppendElement(Substring(entryName, entryNameLen));
+    }
+    prefEntries.Sort();
+    for (uint32_t i = prefEntries.Length(); i--; ) {
+      rv = pref_ReadPrefFromJar(appJarReader, prefEntries[i].get());
+      if (NS_FAILED(rv))
+        NS_WARNING("Error parsing preferences.");
+    }
+  }
+
+  rv = pref_LoadPrefsInDirList(NS_APP_PREFS_DEFAULTS_DIR_LIST);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  NS_CreateServicesFromCategory(NS_PREFSERVICE_APPDEFAULTS_TOPIC_ID,
+                                nullptr, NS_PREFSERVICE_APPDEFAULTS_TOPIC_ID);
+
+  nsCOMPtr<nsIObserverService> observerService =
+    mozilla::services::GetObserverService();
+  if (!observerService)
+    return NS_ERROR_FAILURE;
+
+  observerService->NotifyObservers(nullptr, NS_PREFSERVICE_APPDEFAULTS_TOPIC_ID, nullptr);
+
+  return pref_LoadPrefsInDirList(NS_EXT_PREFS_DEFAULTS_DIR_LIST);
+}
+
+
+/******************************************************************************
+ *
+ * static utilities
+ *
+ ******************************************************************************/
+
+// static
+nsresult
+Preferences::GetBool(const char* aPref, bool* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_GetBoolPref(aPref, aResult, false);
+}
+
+// static
+nsresult
+Preferences::GetInt(const char* aPref, int32_t* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_GetIntPref(aPref, aResult, false);
+}
+
+// static
+nsresult
+Preferences::GetFloat(const char* aPref, float* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  nsAutoCString result;
+  nsresult rv = PREF_CopyCharPref(aPref, getter_Copies(result), false);
+  if (NS_SUCCEEDED(rv)) {
+    *aResult = result.ToFloat(&rv);
+  }
+
+  return rv;
+}
+
+// static
+nsAdoptingCString
+Preferences::GetCString(const char* aPref)
+{
+  nsAdoptingCString result;
+  PREF_CopyCharPref(aPref, getter_Copies(result), false);
+  return result;
+}
+
+// static
+nsAdoptingString
+Preferences::GetString(const char* aPref)
+{
+  nsAdoptingString result;
+  GetString(aPref, &result);
+  return result;
+}
+
+// static
+nsresult
+Preferences::GetCString(const char* aPref, nsACString* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  nsAutoCString result;
+  nsresult rv = PREF_CopyCharPref(aPref, getter_Copies(result), false);
+  if (NS_SUCCEEDED(rv)) {
+    *aResult = result;
+  }
+  return rv;
+}
+
+// static
+nsresult
+Preferences::GetString(const char* aPref, nsAString* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  nsAutoCString result;
+  nsresult rv = PREF_CopyCharPref(aPref, getter_Copies(result), false);
+  if (NS_SUCCEEDED(rv)) {
+    CopyUTF8toUTF16(result, *aResult);
+  }
+  return rv;
+}
+
+// static
+nsAdoptingCString
+Preferences::GetLocalizedCString(const char* aPref)
+{
+  nsAdoptingCString result;
+  GetLocalizedCString(aPref, &result);
+  return result;
+}
+
+// static
+nsAdoptingString
+Preferences::GetLocalizedString(const char* aPref)
+{
+  nsAdoptingString result;
+  GetLocalizedString(aPref, &result);
+  return result;
+}
+
+// static
+nsresult
+Preferences::GetLocalizedCString(const char* aPref, nsACString* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  nsAutoString result;
+  nsresult rv = GetLocalizedString(aPref, &result);
+  if (NS_SUCCEEDED(rv)) {
+    CopyUTF16toUTF8(result, *aResult);
+  }
+  return rv;
+}
+
+// static
+nsresult
+Preferences::GetLocalizedString(const char* aPref, nsAString* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  nsCOMPtr<nsIPrefLocalizedString> prefLocalString;
+  nsresult rv = sRootBranch->GetComplexValue(aPref,
+                                             NS_GET_IID(nsIPrefLocalizedString),
+                                             getter_AddRefs(prefLocalString));
+  if (NS_SUCCEEDED(rv)) {
+    NS_ASSERTION(prefLocalString, "Succeeded but the result is NULL");
+    prefLocalString->GetData(getter_Copies(*aResult));
+  }
+  return rv;
+}
+
+// static
+nsresult
+Preferences::GetComplex(const char* aPref, const nsIID &aType, void** aResult)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return sRootBranch->GetComplexValue(aPref, aType, aResult);
+}
+
+// static
+nsresult
+Preferences::SetCString(const char* aPref, const char* aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetCString from content process:", aPref);
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_SetCharPref(aPref, aValue, false);
+}
+
+// static
+nsresult
+Preferences::SetCString(const char* aPref, const nsACString &aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetCString from content process:", aPref);
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_SetCharPref(aPref, PromiseFlatCString(aValue).get(), false);
+}
+
+// static
+nsresult
+Preferences::SetString(const char* aPref, const char16ptr_t aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetString from content process:", aPref);
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_SetCharPref(aPref, NS_ConvertUTF16toUTF8(aValue).get(), false);
+}
+
+// static
+nsresult
+Preferences::SetString(const char* aPref, const nsAString &aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetString from content process:", aPref);
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_SetCharPref(aPref, NS_ConvertUTF16toUTF8(aValue).get(), false);
+}
+
+// static
+nsresult
+Preferences::SetBool(const char* aPref, bool aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetBool from content process:", aPref);
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_SetBoolPref(aPref, aValue, false);
+}
+
+// static
+nsresult
+Preferences::SetInt(const char* aPref, int32_t aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetInt from content process:", aPref);
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_SetIntPref(aPref, aValue, false);
+}
+
+// static
+nsresult
+Preferences::SetFloat(const char* aPref, float aValue)
+{
+  return SetCString(aPref, nsPrintfCString("%f", aValue).get());
+}
+
+// static
+nsresult
+Preferences::SetComplex(const char* aPref, const nsIID &aType,
+                        nsISupports* aValue)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return sRootBranch->SetComplexValue(aPref, aType, aValue);
+}
+
+// static
+nsresult
+Preferences::ClearUser(const char* aPref)
+{
+  ENSURE_MAIN_PROCESS("Cannot ClearUser from content process:", aPref);
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_ClearUserPref(aPref);
+}
+
+// static
+bool
+Preferences::HasUserValue(const char* aPref)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), false);
+  return PREF_HasUserPref(aPref);
+}
+
+// static
+int32_t
+Preferences::GetType(const char* aPref)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), nsIPrefBranch::PREF_INVALID);
+  int32_t result;
+  return NS_SUCCEEDED(sRootBranch->GetPrefType(aPref, &result)) ?
+    result : nsIPrefBranch::PREF_INVALID;
+}
+
+// static
+nsresult
+Preferences::AddStrongObserver(nsIObserver* aObserver,
+                               const char* aPref)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return sRootBranch->AddObserver(aPref, aObserver, false);
+}
+
+// static
+nsresult
+Preferences::AddWeakObserver(nsIObserver* aObserver,
+                             const char* aPref)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return sRootBranch->AddObserver(aPref, aObserver, true);
+}
+
+// static
+nsresult
+Preferences::RemoveObserver(nsIObserver* aObserver,
+                            const char* aPref)
+{
+  if (!sPreferences && sShutdown) {
+    return NS_OK; // Observers have been released automatically.
+  }
+  NS_ENSURE_TRUE(sPreferences, NS_ERROR_NOT_AVAILABLE);
+  return sRootBranch->RemoveObserver(aPref, aObserver);
+}
+
+// static
+nsresult
+Preferences::AddStrongObservers(nsIObserver* aObserver,
+                                const char** aPrefs)
+{
+  for (uint32_t i = 0; aPrefs[i]; i++) {
+    nsresult rv = AddStrongObserver(aObserver, aPrefs[i]);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  return NS_OK;
+}
+
+// static
+nsresult
+Preferences::AddWeakObservers(nsIObserver* aObserver,
+                              const char** aPrefs)
+{
+  for (uint32_t i = 0; aPrefs[i]; i++) {
+    nsresult rv = AddWeakObserver(aObserver, aPrefs[i]);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  return NS_OK;
+}
+
+// static
+nsresult
+Preferences::RemoveObservers(nsIObserver* aObserver,
+                             const char** aPrefs)
+{
+  if (!sPreferences && sShutdown) {
+    return NS_OK; // Observers have been released automatically.
+  }
+  NS_ENSURE_TRUE(sPreferences, NS_ERROR_NOT_AVAILABLE);
+
+  for (uint32_t i = 0; aPrefs[i]; i++) {
+    nsresult rv = RemoveObserver(aObserver, aPrefs[i]);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  return NS_OK;
+}
+
+// static
+nsresult
+Preferences::RegisterCallback(PrefChangedFunc aCallback,
+                              const char* aPref,
+                              void* aClosure,
+                              MatchKind aMatchKind)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+
+  ValueObserverHashKey hashKey(aPref, aCallback, aMatchKind);
+  RefPtr<ValueObserver> observer;
+  gObserverTable->Get(&hashKey, getter_AddRefs(observer));
+  if (observer) {
+    observer->AppendClosure(aClosure);
+    return NS_OK;
+  }
+
+  observer = new ValueObserver(aPref, aCallback, aMatchKind);
+  observer->AppendClosure(aClosure);
+  nsresult rv = AddStrongObserver(observer, aPref);
+  NS_ENSURE_SUCCESS(rv, rv);
+  gObserverTable->Put(observer, observer);
+  return NS_OK;
+}
+
+// static
+nsresult
+Preferences::RegisterCallbackAndCall(PrefChangedFunc aCallback,
+                                     const char* aPref,
+                                     void* aClosure,
+                                     MatchKind aMatchKind)
+{
+  nsresult rv = RegisterCallback(aCallback, aPref, aClosure, aMatchKind);
+  if (NS_SUCCEEDED(rv)) {
+    (*aCallback)(aPref, aClosure);
+  }
+  return rv;
+}
+
+// static
+nsresult
+Preferences::UnregisterCallback(PrefChangedFunc aCallback,
+                                const char* aPref,
+                                void* aClosure,
+                                MatchKind aMatchKind)
+{
+  if (!sPreferences && sShutdown) {
+    return NS_OK; // Observers have been released automatically.
+  }
+  NS_ENSURE_TRUE(sPreferences, NS_ERROR_NOT_AVAILABLE);
+
+  ValueObserverHashKey hashKey(aPref, aCallback, aMatchKind);
+  RefPtr<ValueObserver> observer;
+  gObserverTable->Get(&hashKey, getter_AddRefs(observer));
+  if (!observer) {
+    return NS_OK;
+  }
+
+  observer->RemoveClosure(aClosure);
+  if (observer->HasNoClosures()) {
+    // Delete the callback since its list of closures is empty.
+    gObserverTable->Remove(observer);
+  }
+  return NS_OK;
+}
+
+static void BoolVarChanged(const char* aPref, void* aClosure)
+{
+  CacheData* cache = static_cast<CacheData*>(aClosure);
+  *((bool*)cache->cacheLocation) =
+    Preferences::GetBool(aPref, cache->defaultValueBool);
+}
+
+// static
+nsresult
+Preferences::AddBoolVarCache(bool* aCache,
+                             const char* aPref,
+                             bool aDefault)
+{
+  NS_ASSERTION(aCache, "aCache must not be NULL");
+#ifdef DEBUG
+  AssertNotAlreadyCached("bool", aPref, aCache);
+#endif
+  *aCache = GetBool(aPref, aDefault);
+  CacheData* data = new CacheData();
+  data->cacheLocation = aCache;
+  data->defaultValueBool = aDefault;
+  gCacheData->AppendElement(data);
+  return RegisterCallback(BoolVarChanged, aPref, data, ExactMatch);
+}
+
+static void IntVarChanged(const char* aPref, void* aClosure)
+{
+  CacheData* cache = static_cast<CacheData*>(aClosure);
+  *((int32_t*)cache->cacheLocation) =
+    Preferences::GetInt(aPref, cache->defaultValueInt);
+}
+
+// static
+nsresult
+Preferences::AddIntVarCache(int32_t* aCache,
+                            const char* aPref,
+                            int32_t aDefault)
+{
+  NS_ASSERTION(aCache, "aCache must not be NULL");
+#ifdef DEBUG
+  AssertNotAlreadyCached("int", aPref, aCache);
+#endif
+  *aCache = Preferences::GetInt(aPref, aDefault);
+  CacheData* data = new CacheData();
+  data->cacheLocation = aCache;
+  data->defaultValueInt = aDefault;
+  gCacheData->AppendElement(data);
+  return RegisterCallback(IntVarChanged, aPref, data, ExactMatch);
+}
+
+static void UintVarChanged(const char* aPref, void* aClosure)
+{
+  CacheData* cache = static_cast<CacheData*>(aClosure);
+  *((uint32_t*)cache->cacheLocation) =
+    Preferences::GetUint(aPref, cache->defaultValueUint);
+}
+
+// static
+nsresult
+Preferences::AddUintVarCache(uint32_t* aCache,
+                             const char* aPref,
+                             uint32_t aDefault)
+{
+  NS_ASSERTION(aCache, "aCache must not be NULL");
+#ifdef DEBUG
+  AssertNotAlreadyCached("uint", aPref, aCache);
+#endif
+  *aCache = Preferences::GetUint(aPref, aDefault);
+  CacheData* data = new CacheData();
+  data->cacheLocation = aCache;
+  data->defaultValueUint = aDefault;
+  gCacheData->AppendElement(data);
+  return RegisterCallback(UintVarChanged, aPref, data, ExactMatch);
+}
+
+template <MemoryOrdering Order>
+static void AtomicUintVarChanged(const char* aPref, void* aClosure)
+{
+  CacheData* cache = static_cast<CacheData*>(aClosure);
+  *((Atomic<uint32_t, Order>*)cache->cacheLocation) =
+    Preferences::GetUint(aPref, cache->defaultValueUint);
+}
+
+template <MemoryOrdering Order>
+// static
+nsresult
+Preferences::AddAtomicUintVarCache(Atomic<uint32_t, Order>* aCache,
+                                   const char* aPref,
+                                   uint32_t aDefault)
+{
+  NS_ASSERTION(aCache, "aCache must not be NULL");
+#ifdef DEBUG
+  AssertNotAlreadyCached("uint", aPref, aCache);
+#endif
+  *aCache = Preferences::GetUint(aPref, aDefault);
+  CacheData* data = new CacheData();
+  data->cacheLocation = aCache;
+  data->defaultValueUint = aDefault;
+  gCacheData->AppendElement(data);
+  return RegisterCallback(AtomicUintVarChanged<Order>, aPref, data, ExactMatch);
+}
+
+// Since the definition of this template function is not in a header file,
+// we need to explicitly specify the instantiations that are required.
+// Currently only the order=Relaxed variant is needed.
+template
+nsresult Preferences::AddAtomicUintVarCache(Atomic<uint32_t,Relaxed>*,
+                                            const char*, uint32_t);
+
+static void FloatVarChanged(const char* aPref, void* aClosure)
+{
+  CacheData* cache = static_cast<CacheData*>(aClosure);
+  *((float*)cache->cacheLocation) =
+    Preferences::GetFloat(aPref, cache->defaultValueFloat);
+}
+
+// static
+nsresult
+Preferences::AddFloatVarCache(float* aCache,
+                             const char* aPref,
+                             float aDefault)
+{
+  NS_ASSERTION(aCache, "aCache must not be NULL");
+#ifdef DEBUG
+  AssertNotAlreadyCached("float", aPref, aCache);
+#endif
+  *aCache = Preferences::GetFloat(aPref, aDefault);
+  CacheData* data = new CacheData();
+  data->cacheLocation = aCache;
+  data->defaultValueFloat = aDefault;
+  gCacheData->AppendElement(data);
+  return RegisterCallback(FloatVarChanged, aPref, data, ExactMatch);
+}
+
+// static
+nsresult
+Preferences::GetDefaultBool(const char* aPref, bool* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_GetBoolPref(aPref, aResult, true);
+}
+
+// static
+nsresult
+Preferences::GetDefaultInt(const char* aPref, int32_t* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return PREF_GetIntPref(aPref, aResult, true);
+}
+
+// static
+nsresult
+Preferences::GetDefaultCString(const char* aPref, nsACString* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  nsAutoCString result;
+  nsresult rv = PREF_CopyCharPref(aPref, getter_Copies(result), true);
+  if (NS_SUCCEEDED(rv)) {
+    *aResult = result;
+  }
+  return rv;
+}
+
+// static
+nsresult
+Preferences::GetDefaultString(const char* aPref, nsAString* aResult)
+{
+  NS_PRECONDITION(aResult, "aResult must not be NULL");
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  nsAutoCString result;
+  nsresult rv = PREF_CopyCharPref(aPref, getter_Copies(result), true);
+  if (NS_SUCCEEDED(rv)) {
+    CopyUTF8toUTF16(result, *aResult);
+  }
+  return rv;
+}
+
+// static
+nsresult
+Preferences::GetDefaultLocalizedCString(const char* aPref,
+                                        nsACString* aResult)
+{
+  nsAutoString result;
+  nsresult rv = GetDefaultLocalizedString(aPref, &result);
+  if (NS_SUCCEEDED(rv)) {
+    CopyUTF16toUTF8(result, *aResult);
+  }
+  return rv;
+}
+
+// static
+nsresult
+Preferences::GetDefaultLocalizedString(const char* aPref,
+                                       nsAString* aResult)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  nsCOMPtr<nsIPrefLocalizedString> prefLocalString;
+  nsresult rv =
+    sDefaultRootBranch->GetComplexValue(aPref,
+                                        NS_GET_IID(nsIPrefLocalizedString),
+                                        getter_AddRefs(prefLocalString));
+  if (NS_SUCCEEDED(rv)) {
+    NS_ASSERTION(prefLocalString, "Succeeded but the result is NULL");
+    prefLocalString->GetData(getter_Copies(*aResult));
+  }
+  return rv;
+}
+
+// static
+nsAdoptingString
+Preferences::GetDefaultString(const char* aPref)
+{
+  nsAdoptingString result;
+  GetDefaultString(aPref, &result);
+  return result;
+}
+
+// static
+nsAdoptingCString
+Preferences::GetDefaultCString(const char* aPref)
+{
+  nsAdoptingCString result;
+  PREF_CopyCharPref(aPref, getter_Copies(result), true);
+  return result;
+}
+
+// static
+nsAdoptingString
+Preferences::GetDefaultLocalizedString(const char* aPref)
+{
+  nsAdoptingString result;
+  GetDefaultLocalizedString(aPref, &result);
+  return result;
+}
+
+// static
+nsAdoptingCString
+Preferences::GetDefaultLocalizedCString(const char* aPref)
+{
+  nsAdoptingCString result;
+  GetDefaultLocalizedCString(aPref, &result);
+  return result;
+}
+
+// static
+nsresult
+Preferences::GetDefaultComplex(const char* aPref, const nsIID &aType,
+                               void** aResult)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
+  return sDefaultRootBranch->GetComplexValue(aPref, aType, aResult);
+}
+
+// static
+int32_t
+Preferences::GetDefaultType(const char* aPref)
+{
+  NS_ENSURE_TRUE(InitStaticMembers(), nsIPrefBranch::PREF_INVALID);
+  int32_t result;
+  return NS_SUCCEEDED(sDefaultRootBranch->GetPrefType(aPref, &result)) ?
+    result : nsIPrefBranch::PREF_INVALID;
+}
+
+} // namespace mozilla
+
+#undef ENSURE_MAIN_PROCESS
diff --git a/components/preferences/src/Preferences.h b/components/preferences/src/Preferences.h
new file mode 100644
index 000000000..255d2a8d2
--- /dev/null
+++ b/components/preferences/src/Preferences.h
@@ -0,0 +1,408 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_Preferences_h
+#define mozilla_Preferences_h
+
+#ifndef MOZILLA_INTERNAL_API
+#error "This header is only usable from within libxul (MOZILLA_INTERNAL_API)."
+#endif
+
+#include "nsIPrefService.h"
+#include "nsIPrefBranch.h"
+#include "nsIPrefBranchInternal.h"
+#include "nsIObserver.h"
+#include "nsCOMPtr.h"
+#include "nsTArray.h"
+#include "nsWeakReference.h"
+#include "mozilla/MemoryReporting.h"
+
+class nsIFile;
+class nsAdoptingString;
+class nsAdoptingCString;
+
+#ifndef have_PrefChangedFunc_typedef
+typedef void (*PrefChangedFunc)(const char *, void *);
+#define have_PrefChangedFunc_typedef
+#endif
+
+namespace mozilla {
+
+namespace dom {
+class PrefSetting;
+} // namespace dom
+
+class Preferences final : public nsIPrefService,
+                          public nsIObserver,
+                          public nsIPrefBranchInternal,
+                          public nsSupportsWeakReference
+{
+public:
+  typedef mozilla::dom::PrefSetting PrefSetting;
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIPREFSERVICE
+  NS_FORWARD_NSIPREFBRANCH(sRootBranch->)
+  NS_DECL_NSIOBSERVER
+
+  Preferences();
+
+  nsresult Init();
+
+  /**
+   * Returns true if the Preferences service is available, false otherwise.
+   */
+  static bool IsServiceAvailable();
+
+  /**
+   * Reset loaded user prefs then read them
+   */
+  static nsresult ResetAndReadUserPrefs();
+
+  /**
+   * Returns the singleton instance which is addreffed.
+   */
+  static Preferences* GetInstanceForService();
+
+  /**
+   * Finallizes global members.
+   */
+  static void Shutdown();
+
+  /**
+   * Returns shared pref service instance
+   * NOTE: not addreffed.
+   */
+  static nsIPrefService* GetService()
+  {
+    NS_ENSURE_TRUE(InitStaticMembers(), nullptr);
+    return sPreferences;
+  }
+
+  /**
+   * Returns shared pref branch instance.
+   * NOTE: not addreffed.
+   */
+  static nsIPrefBranch* GetRootBranch()
+  {
+    NS_ENSURE_TRUE(InitStaticMembers(), nullptr);
+    return sRootBranch;
+  }
+
+  /**
+   * Returns shared default pref branch instance.
+   * NOTE: not addreffed.
+   */
+  static nsIPrefBranch* GetDefaultRootBranch()
+  {
+    NS_ENSURE_TRUE(InitStaticMembers(), nullptr);
+    return sDefaultRootBranch;
+  }
+
+  /**
+   * Gets int or bool type pref value with default value if failed to get
+   * the pref.
+   */
+  static bool GetBool(const char* aPref, bool aDefault = false)
+  {
+    bool result = aDefault;
+    GetBool(aPref, &result);
+    return result;
+  }
+
+  static int32_t GetInt(const char* aPref, int32_t aDefault = 0)
+  {
+    int32_t result = aDefault;
+    GetInt(aPref, &result);
+    return result;
+  }
+
+  static uint32_t GetUint(const char* aPref, uint32_t aDefault = 0)
+  {
+    uint32_t result = aDefault;
+    GetUint(aPref, &result);
+    return result;
+  }
+
+  static float GetFloat(const char* aPref, float aDefault = 0)
+  {
+    float result = aDefault;
+    GetFloat(aPref, &result);
+    return result;
+  }
+
+  /**
+   * Gets char type pref value directly.  If failed, the get() of result
+   * returns nullptr.  Even if succeeded but the result was empty string, the
+   * get() does NOT return nullptr.  So, you can check whether the method
+   * succeeded or not by:
+   *
+   * nsAdoptingString value = Prefereces::GetString("foo.bar");
+   * if (!value) {
+   *   // failed
+   * }
+   *
+   * Be aware.  If you wrote as:
+   *
+   * nsAutoString value = Preferences::GetString("foo.bar");
+   * if (!value.get()) {
+   *   // the condition is always FALSE!!
+   * }
+   *
+   * The value.get() doesn't return nullptr. You must use nsAdoptingString
+   * when you need to check whether it was failure or not.
+   */
+  static nsAdoptingCString GetCString(const char* aPref);
+  static nsAdoptingString GetString(const char* aPref);
+  static nsAdoptingCString GetLocalizedCString(const char* aPref);
+  static nsAdoptingString GetLocalizedString(const char* aPref);
+
+  /**
+   * Gets int, float, or bool type pref value with raw return value of
+   * nsIPrefBranch.
+   *
+   * @param aPref       A pref name.
+   * @param aResult     Must not be nullptr.  The value is never modified
+   *                    when these methods fail.
+   */
+  static nsresult GetBool(const char* aPref, bool* aResult);
+  static nsresult GetInt(const char* aPref, int32_t* aResult);
+  static nsresult GetFloat(const char* aPref, float* aResult);
+  static nsresult GetUint(const char* aPref, uint32_t* aResult)
+  {
+    int32_t result;
+    nsresult rv = GetInt(aPref, &result);
+    if (NS_SUCCEEDED(rv)) {
+      *aResult = static_cast<uint32_t>(result);
+    }
+    return rv;
+  }
+
+  /**
+   * Gets string type pref value with raw return value of nsIPrefBranch.
+   *
+   * @param aPref       A pref name.
+   * @param aResult     Must not be nullptr.  The value is never modified
+   *                    when these methods fail.
+   */
+  static nsresult GetCString(const char* aPref, nsACString* aResult);
+  static nsresult GetString(const char* aPref, nsAString* aResult);
+  static nsresult GetLocalizedCString(const char* aPref, nsACString* aResult);
+  static nsresult GetLocalizedString(const char* aPref, nsAString* aResult);
+
+  static nsresult GetComplex(const char* aPref, const nsIID &aType,
+                             void** aResult);
+
+  /**
+   * Sets various type pref values.
+   */
+  static nsresult SetBool(const char* aPref, bool aValue);
+  static nsresult SetInt(const char* aPref, int32_t aValue);
+  static nsresult SetUint(const char* aPref, uint32_t aValue)
+  {
+    return SetInt(aPref, static_cast<int32_t>(aValue));
+  }
+  static nsresult SetFloat(const char* aPref, float aValue);
+  static nsresult SetCString(const char* aPref, const char* aValue);
+  static nsresult SetCString(const char* aPref, const nsACString &aValue);
+  static nsresult SetString(const char* aPref, const char16ptr_t aValue);
+  static nsresult SetString(const char* aPref, const nsAString &aValue);
+
+  static nsresult SetComplex(const char* aPref, const nsIID &aType,
+                             nsISupports* aValue);
+
+  /**
+   * Clears user set pref.
+   */
+  static nsresult ClearUser(const char* aPref);
+
+  /**
+   * Whether the pref has a user value or not.
+   */
+  static bool HasUserValue(const char* aPref);
+
+  /**
+   * Gets the type of the pref.
+   */
+  static int32_t GetType(const char* aPref);
+
+  /**
+   * Adds/Removes the observer for the root pref branch.
+   * The observer is referenced strongly if AddStrongObserver is used.  On the
+   * other hand, it is referenced weakly, if AddWeakObserver is used.
+   * See nsIPrefBranch.idl for details.
+   */
+  static nsresult AddStrongObserver(nsIObserver* aObserver, const char* aPref);
+  static nsresult AddWeakObserver(nsIObserver* aObserver, const char* aPref);
+  static nsresult RemoveObserver(nsIObserver* aObserver, const char* aPref);
+
+  /**
+   * Adds/Removes two or more observers for the root pref branch.
+   * Pass to aPrefs an array of const char* whose last item is nullptr.
+   */
+  static nsresult AddStrongObservers(nsIObserver* aObserver,
+                                     const char** aPrefs);
+  static nsresult AddWeakObservers(nsIObserver* aObserver,
+                                   const char** aPrefs);
+  static nsresult RemoveObservers(nsIObserver* aObserver,
+                                  const char** aPrefs);
+
+  /**
+   * Registers/Unregisters the callback function for the aPref.
+   *
+   * Pass ExactMatch for aMatchKind to only get callbacks for
+   * exact matches and not prefixes.
+   */
+  enum MatchKind {
+    PrefixMatch,
+    ExactMatch,
+  };
+  static nsresult RegisterCallback(PrefChangedFunc aCallback,
+                                   const char* aPref,
+                                   void* aClosure = nullptr,
+                                   MatchKind aMatchKind = PrefixMatch);
+  static nsresult UnregisterCallback(PrefChangedFunc aCallback,
+                                     const char* aPref,
+                                     void* aClosure = nullptr,
+                                     MatchKind aMatchKind = PrefixMatch);
+  // Like RegisterCallback, but also calls the callback immediately for
+  // initialization.
+  static nsresult RegisterCallbackAndCall(PrefChangedFunc aCallback,
+                                          const char* aPref,
+                                          void* aClosure = nullptr,
+                                          MatchKind aMatchKind = PrefixMatch);
+
+  /**
+   * Adds the aVariable to cache table.  aVariable must be a pointer for a
+   * static variable.  The value will be modified when the pref value is
+   * changed but note that even if you modified it, the value isn't assigned to
+   * the pref.
+   */
+  static nsresult AddBoolVarCache(bool* aVariable,
+                                  const char* aPref,
+                                  bool aDefault = false);
+  static nsresult AddIntVarCache(int32_t* aVariable,
+                                 const char* aPref,
+                                 int32_t aDefault = 0);
+  static nsresult AddUintVarCache(uint32_t* aVariable,
+                                  const char* aPref,
+                                  uint32_t aDefault = 0);
+  template <MemoryOrdering Order>
+  static nsresult AddAtomicUintVarCache(Atomic<uint32_t, Order>* aVariable,
+                                        const char* aPref,
+                                        uint32_t aDefault = 0);
+  static nsresult AddFloatVarCache(float* aVariable,
+                                   const char* aPref,
+                                   float aDefault = 0.0f);
+
+  /**
+   * Gets the default bool, int or uint value of the pref.
+   * The result is raw result of nsIPrefBranch::Get*Pref().
+   * If the pref could have any value, you needed to use these methods.
+   * If not so, you could use below methods.
+   */
+  static nsresult GetDefaultBool(const char* aPref, bool* aResult);
+  static nsresult GetDefaultInt(const char* aPref, int32_t* aResult);
+  static nsresult GetDefaultUint(const char* aPref, uint32_t* aResult)
+  {
+    return GetDefaultInt(aPref, reinterpret_cast<int32_t*>(aResult));
+  }
+
+  /**
+   * Gets the default bool, int or uint value of the pref directly.
+   * You can set an invalid value of the pref to aFailedResult.  If these
+   * methods failed to get the default value, they would return the
+   * aFailedResult value.
+   */
+  static bool GetDefaultBool(const char* aPref, bool aFailedResult)
+  {
+    bool result;
+    return NS_SUCCEEDED(GetDefaultBool(aPref, &result)) ? result :
+                                                          aFailedResult;
+  }
+  static int32_t GetDefaultInt(const char* aPref, int32_t aFailedResult)
+  {
+    int32_t result;
+    return NS_SUCCEEDED(GetDefaultInt(aPref, &result)) ? result : aFailedResult;
+  }
+  static uint32_t GetDefaultUint(const char* aPref, uint32_t aFailedResult)
+  {
+   return static_cast<uint32_t>(
+     GetDefaultInt(aPref, static_cast<int32_t>(aFailedResult)));
+  }
+
+  /**
+   * Gets the default value of the char type pref.
+   * If the get() of the result returned nullptr, that meant the value didn't
+   * have default value.
+   *
+   * See the comment at definition at GetString() and GetCString() for more
+   * details of the result.
+   */
+  static nsAdoptingString GetDefaultString(const char* aPref);
+  static nsAdoptingCString GetDefaultCString(const char* aPref);
+  static nsAdoptingString GetDefaultLocalizedString(const char* aPref);
+  static nsAdoptingCString GetDefaultLocalizedCString(const char* aPref);
+
+  static nsresult GetDefaultCString(const char* aPref, nsACString* aResult);
+  static nsresult GetDefaultString(const char* aPref, nsAString* aResult);
+  static nsresult GetDefaultLocalizedCString(const char* aPref,
+                                             nsACString* aResult);
+  static nsresult GetDefaultLocalizedString(const char* aPref,
+                                            nsAString* aResult);
+
+  static nsresult GetDefaultComplex(const char* aPref, const nsIID &aType,
+                                    void** aResult);
+
+  /**
+   * Gets the type of the pref.
+   */
+  static int32_t GetDefaultType(const char* aPref);
+
+  // Used to synchronise preferences between chrome and content processes.
+  static void GetPreferences(InfallibleTArray<PrefSetting>* aPrefs);
+  static void GetPreference(PrefSetting* aPref);
+  static void SetPreference(const PrefSetting& aPref);
+
+  static int64_t SizeOfIncludingThisAndOtherStuff(mozilla::MallocSizeOf aMallocSizeOf);
+
+  static void DirtyCallback();
+
+protected:
+  virtual ~Preferences();
+
+  nsresult NotifyServiceObservers(const char *aSubject);
+  /**
+   * Reads the default pref file or, if that failed, try to save a new one.
+   *
+   * @return NS_OK if either action succeeded,
+   *         or the error code related to the read attempt.
+   */
+  nsresult UseDefaultPrefFile();
+  nsresult UseUserPrefFile();
+  nsresult ReadAndOwnUserPrefFile(nsIFile *aFile);
+  nsresult ReadAndOwnSharedUserPrefFile(nsIFile *aFile);
+  nsresult SavePrefFileInternal(nsIFile* aFile);
+  nsresult WritePrefFile(nsIFile* aFile);
+  nsresult MakeBackupPrefFile(nsIFile *aFile);
+
+private:
+  nsCOMPtr<nsIFile>        mCurrentFile;
+  bool                     mDirty;
+
+  static Preferences*      sPreferences;
+  static nsIPrefBranch*    sRootBranch;
+  static nsIPrefBranch*    sDefaultRootBranch;
+  static bool              sShutdown;
+
+  /**
+   * Init static members.  TRUE if it succeeded.  Otherwise, FALSE.
+   */
+  static bool InitStaticMembers();
+};
+
+} // namespace mozilla
+
+#endif // mozilla_Preferences_h
diff --git a/components/preferences/src/nsPrefBranch.cpp b/components/preferences/src/nsPrefBranch.cpp
new file mode 100644
index 000000000..6107e64d8
--- /dev/null
+++ b/components/preferences/src/nsPrefBranch.cpp
@@ -0,0 +1,943 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/ContentChild.h"
+#include "nsXULAppAPI.h"
+
+#include "nsPrefBranch.h"
+#include "nsILocalFile.h" // nsILocalFile used for backwards compatibility
+#include "nsIObserverService.h"
+#include "nsXPCOM.h"
+#include "nsISupportsPrimitives.h"
+#include "nsIDirectoryService.h"
+#include "nsString.h"
+#include "nsReadableUtils.h"
+#include "nsXPIDLString.h"
+#include "nsPrintfCString.h"
+#include "nsIStringBundle.h"
+#include "prefapi.h"
+#include "PLDHashTable.h"
+
+#include "nsCRT.h"
+#include "mozilla/Services.h"
+
+#include "prefapi_private_data.h"
+
+#include "nsIConsoleService.h"
+
+#ifdef DEBUG
+#define ENSURE_MAIN_PROCESS(message, pref) do {                                \
+  if (GetContentChild()) {                                                     \
+    nsPrintfCString msg("ENSURE_MAIN_PROCESS failed. %s %s", message, pref);   \
+    NS_ERROR(msg.get());                                                       \
+    return NS_ERROR_NOT_AVAILABLE;                                             \
+  }                                                                            \
+} while (0);
+#else
+#define ENSURE_MAIN_PROCESS(message, pref)                                     \
+  if (GetContentChild()) {                                                     \
+    return NS_ERROR_NOT_AVAILABLE;                                             \
+  }
+#endif
+
+using mozilla::dom::ContentChild;
+
+static ContentChild*
+GetContentChild()
+{
+  if (XRE_IsContentProcess()) {
+    ContentChild* cpc = ContentChild::GetSingleton();
+    if (!cpc) {
+      NS_RUNTIMEABORT("Content Protocol is NULL!  We're going to crash!");
+    }
+    return cpc;
+  }
+  return nullptr;
+}
+
+/*
+ * Constructor/Destructor
+ */
+
+nsPrefBranch::nsPrefBranch(const char *aPrefRoot, bool aDefaultBranch)
+{
+  mPrefRoot = aPrefRoot;
+  mPrefRootLength = mPrefRoot.Length();
+  mIsDefault = aDefaultBranch;
+  mFreeingObserverList = false;
+
+  nsCOMPtr<nsIObserverService> observerService =
+    mozilla::services::GetObserverService();
+  if (observerService) {
+    ++mRefCnt;    // Our refcnt must be > 0 when we call this, or we'll get deleted!
+    // add weak so we don't have to clean up at shutdown
+    observerService->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, true);
+    --mRefCnt;
+  }
+}
+
+nsPrefBranch::~nsPrefBranch()
+{
+  freeObserverList();
+
+  nsCOMPtr<nsIObserverService> observerService =
+    mozilla::services::GetObserverService();
+  if (observerService)
+    observerService->RemoveObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID);
+}
+
+
+/*
+ * nsISupports Implementation
+ */
+
+NS_IMPL_ADDREF(nsPrefBranch)
+NS_IMPL_RELEASE(nsPrefBranch)
+
+NS_INTERFACE_MAP_BEGIN(nsPrefBranch)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIPrefBranch)
+  NS_INTERFACE_MAP_ENTRY(nsIPrefBranch)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIPrefBranch2, !mIsDefault)
+  NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsIPrefBranchInternal, !mIsDefault)
+  NS_INTERFACE_MAP_ENTRY(nsIObserver)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+NS_INTERFACE_MAP_END
+
+
+/*
+ * nsIPrefBranch Implementation
+ */
+
+NS_IMETHODIMP nsPrefBranch::GetRoot(char **aRoot)
+{
+  NS_ENSURE_ARG_POINTER(aRoot);
+  mPrefRoot.Truncate(mPrefRootLength);
+  *aRoot = ToNewCString(mPrefRoot);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsPrefBranch::GetPrefType(const char *aPrefName, int32_t *_retval)
+{
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  switch (PREF_GetPrefType(pref)) {
+    case PrefType::String:
+      *_retval = PREF_STRING;
+      break;
+    case PrefType::Int:
+      *_retval = PREF_INT;
+      break;
+    case PrefType::Bool:
+      *_retval = PREF_BOOL;
+        break;
+    case PrefType::Invalid:
+    default:
+      *_retval = PREF_INVALID;
+      break;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsPrefBranch::GetBoolPrefWithDefault(const char *aPrefName,
+                                                   bool aDefaultValue,
+                                                   uint8_t _argc, bool *_retval)
+{
+  nsresult rv = GetBoolPref(aPrefName, _retval);
+
+  if (NS_FAILED(rv) && _argc == 1) {
+    *_retval = aDefaultValue;
+    return NS_OK;
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP nsPrefBranch::GetBoolPref(const char *aPrefName, bool *_retval)
+{
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_GetBoolPref(pref, _retval, mIsDefault);
+}
+
+NS_IMETHODIMP nsPrefBranch::SetBoolPref(const char *aPrefName, bool aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetBoolPref from content process:", aPrefName);
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_SetBoolPref(pref, aValue, mIsDefault);
+}
+
+NS_IMETHODIMP nsPrefBranch::GetFloatPrefWithDefault(const char *aPrefName,
+                                                    float aDefaultValue,
+                                                    uint8_t _argc, float *_retval)
+{
+  nsresult rv = GetFloatPref(aPrefName, _retval);
+
+  if (NS_FAILED(rv) && _argc == 1) {
+    *_retval = aDefaultValue;
+    return NS_OK;
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP nsPrefBranch::GetFloatPref(const char *aPrefName, float *_retval)
+{
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  nsAutoCString stringVal;
+  nsresult rv = GetCharPref(pref, getter_Copies(stringVal));
+  if (NS_SUCCEEDED(rv)) {
+    *_retval = stringVal.ToFloat(&rv);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP nsPrefBranch::GetCharPrefWithDefault(const char *aPrefName,
+                                                   const char *aDefaultValue,
+                                                   uint8_t _argc, char **_retval)
+{
+  nsresult rv = GetCharPref(aPrefName, _retval);
+
+  if (NS_FAILED(rv) && _argc == 1) {
+    NS_ENSURE_ARG(aDefaultValue);
+    *_retval = NS_strdup(aDefaultValue);
+    return NS_OK;
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP nsPrefBranch::GetCharPref(const char *aPrefName, char **_retval)
+{
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_CopyCharPref(pref, _retval, mIsDefault);
+}
+
+NS_IMETHODIMP nsPrefBranch::SetCharPref(const char *aPrefName, const char *aValue)
+{
+  nsresult rv = CheckSanityOfStringLength(aPrefName, aValue);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  return SetCharPrefInternal(aPrefName, aValue);
+}
+
+nsresult nsPrefBranch::SetCharPrefInternal(const char *aPrefName, const char *aValue)
+
+{
+  ENSURE_MAIN_PROCESS("Cannot SetCharPref from content process:", aPrefName);
+  NS_ENSURE_ARG(aPrefName);
+  NS_ENSURE_ARG(aValue);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_SetCharPref(pref, aValue, mIsDefault);
+}
+
+NS_IMETHODIMP nsPrefBranch::GetIntPrefWithDefault(const char *aPrefName,
+                                                  int32_t aDefaultValue,
+                                                  uint8_t _argc, int32_t *_retval)
+{
+  nsresult rv = GetIntPref(aPrefName, _retval);
+
+  if (NS_FAILED(rv) && _argc == 1) {
+    *_retval = aDefaultValue;
+    return NS_OK;
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP nsPrefBranch::GetIntPref(const char *aPrefName, int32_t *_retval)
+{
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_GetIntPref(pref, _retval, mIsDefault);
+}
+
+NS_IMETHODIMP nsPrefBranch::SetIntPref(const char *aPrefName, int32_t aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetIntPref from content process:", aPrefName);
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_SetIntPref(pref, aValue, mIsDefault);
+}
+
+NS_IMETHODIMP nsPrefBranch::GetComplexValue(const char *aPrefName, const nsIID & aType, void **_retval)
+{
+  NS_ENSURE_ARG(aPrefName);
+
+  nsresult       rv;
+  nsXPIDLCString utf8String;
+
+  // we have to do this one first because it's different than all the rest
+  if (aType.Equals(NS_GET_IID(nsIPrefLocalizedString))) {
+    nsCOMPtr<nsIPrefLocalizedString> theString(do_CreateInstance(NS_PREFLOCALIZEDSTRING_CONTRACTID, &rv));
+    if (NS_FAILED(rv)) return rv;
+
+    const char *pref = getPrefName(aPrefName);
+    bool    bNeedDefault = false;
+
+    if (mIsDefault) {
+      bNeedDefault = true;
+    } else {
+      // if there is no user (or locked) value
+      if (!PREF_HasUserPref(pref) && !PREF_PrefIsLocked(pref)) {
+        bNeedDefault = true;
+      }
+    }
+
+    // if we need to fetch the default value, do that instead, otherwise use the
+    // value we pulled in at the top of this function
+    if (bNeedDefault) {
+      nsXPIDLString utf16String;
+      rv = GetDefaultFromPropertiesFile(pref, getter_Copies(utf16String));
+      if (NS_SUCCEEDED(rv)) {
+        theString->SetData(utf16String.get());
+      }
+    } else {
+      rv = GetCharPref(aPrefName, getter_Copies(utf8String));
+      if (NS_SUCCEEDED(rv)) {
+        theString->SetData(NS_ConvertUTF8toUTF16(utf8String).get());
+      }
+    }
+
+    if (NS_SUCCEEDED(rv)) {
+      theString.forget(reinterpret_cast<nsIPrefLocalizedString**>(_retval));
+    }
+
+    return rv;
+  }
+
+  // if we can't get the pref, there's no point in being here
+  rv = GetCharPref(aPrefName, getter_Copies(utf8String));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // also check nsILocalFile, for backwards compatibility
+  if (aType.Equals(NS_GET_IID(nsIFile)) || aType.Equals(NS_GET_IID(nsILocalFile))) {
+    if (GetContentChild()) {
+      NS_ERROR("cannot get nsIFile pref from content process");
+      return NS_ERROR_NOT_AVAILABLE;
+    }
+
+    nsCOMPtr<nsIFile> file(do_CreateInstance(NS_LOCAL_FILE_CONTRACTID, &rv));
+
+    if (NS_SUCCEEDED(rv)) {
+      rv = file->SetPersistentDescriptor(utf8String);
+      if (NS_SUCCEEDED(rv)) {
+        file.forget(reinterpret_cast<nsIFile**>(_retval));
+        return NS_OK;
+      }
+    }
+    return rv;
+  }
+
+  if (aType.Equals(NS_GET_IID(nsIRelativeFilePref))) {
+    if (GetContentChild()) {
+      NS_ERROR("cannot get nsIRelativeFilePref from content process");
+      return NS_ERROR_NOT_AVAILABLE;
+    }
+
+    nsACString::const_iterator keyBegin, strEnd;
+    utf8String.BeginReading(keyBegin);
+    utf8String.EndReading(strEnd);    
+
+    // The pref has the format: [fromKey]a/b/c
+    if (*keyBegin++ != '[')        
+      return NS_ERROR_FAILURE;
+    nsACString::const_iterator keyEnd(keyBegin);
+    if (!FindCharInReadable(']', keyEnd, strEnd))
+      return NS_ERROR_FAILURE;
+    nsAutoCString key(Substring(keyBegin, keyEnd));
+    
+    nsCOMPtr<nsIFile> fromFile;
+    nsCOMPtr<nsIProperties> directoryService(do_GetService(NS_DIRECTORY_SERVICE_CONTRACTID, &rv));
+    if (NS_FAILED(rv))
+      return rv;
+    rv = directoryService->Get(key.get(), NS_GET_IID(nsIFile), getter_AddRefs(fromFile));
+    if (NS_FAILED(rv))
+      return rv;
+    
+    nsCOMPtr<nsIFile> theFile;
+    rv = NS_NewNativeLocalFile(EmptyCString(), true, getter_AddRefs(theFile));
+    if (NS_FAILED(rv))
+      return rv;
+    rv = theFile->SetRelativeDescriptor(fromFile, Substring(++keyEnd, strEnd));
+    if (NS_FAILED(rv))
+      return rv;
+    nsCOMPtr<nsIRelativeFilePref> relativePref;
+    rv = NS_NewRelativeFilePref(theFile, key, getter_AddRefs(relativePref));
+    if (NS_FAILED(rv))
+      return rv;
+
+    relativePref.forget(reinterpret_cast<nsIRelativeFilePref**>(_retval));
+    return NS_OK;
+  }
+
+  if (aType.Equals(NS_GET_IID(nsISupportsString))) {
+    nsCOMPtr<nsISupportsString> theString(do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID, &rv));
+
+    if (NS_SUCCEEDED(rv)) {
+      // Debugging to see why we end up with very long strings here with
+      // some addons, see bug 836263.
+      nsAutoString wdata;
+      if (!AppendUTF8toUTF16(utf8String, wdata, mozilla::fallible)) {
+        NS_RUNTIMEABORT("bug836263");
+      }
+      theString->SetData(wdata);
+      theString.forget(reinterpret_cast<nsISupportsString**>(_retval));
+    }
+    return rv;
+  }
+
+  NS_WARNING("nsPrefBranch::GetComplexValue - Unsupported interface type");
+  return NS_NOINTERFACE;
+}
+
+nsresult nsPrefBranch::CheckSanityOfStringLength(const char* aPrefName, const char* aValue) {
+  if (!aValue) {
+    return NS_OK;
+  }
+  return CheckSanityOfStringLength(aPrefName, strlen(aValue));
+}
+
+nsresult nsPrefBranch::CheckSanityOfStringLength(const char* aPrefName, const nsAString& aValue) {
+  return CheckSanityOfStringLength(aPrefName, aValue.Length());
+}
+
+nsresult nsPrefBranch::CheckSanityOfStringLength(const char* aPrefName, const uint32_t aLength) {
+  if (aLength > MAX_PREF_LENGTH) {
+    return NS_ERROR_ILLEGAL_VALUE;
+  }
+  if (aLength <= MAX_ADVISABLE_PREF_LENGTH) {
+    return NS_OK;
+  }
+  nsresult rv;
+  nsCOMPtr<nsIConsoleService> console = do_GetService("@mozilla.org/consoleservice;1", &rv);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  nsAutoCString message(nsPrintfCString("Warning: attempting to write %d bytes to preference %s. This is bad "
+                                        "for general performance and memory usage. Such an amount of data "
+                                        "should rather be written to an external file. This preference will "
+                                        "not be sent to any content processes.",
+                                        aLength,
+                                        getPrefName(aPrefName)));
+  rv = console->LogStringMessage(NS_ConvertUTF8toUTF16(message).get());
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  return NS_OK;
+}
+
+/*static*/
+void nsPrefBranch::ReportToConsole(const nsAString& aMessage)
+{
+  nsresult rv;
+  nsCOMPtr<nsIConsoleService> console = do_GetService("@mozilla.org/consoleservice;1", &rv);
+  if (NS_FAILED(rv)) {
+    return;
+  }
+  nsAutoString message(aMessage);
+  console->LogStringMessage(message.get());
+}
+
+NS_IMETHODIMP nsPrefBranch::SetComplexValue(const char *aPrefName, const nsIID & aType, nsISupports *aValue)
+{
+  ENSURE_MAIN_PROCESS("Cannot SetComplexValue from content process:", aPrefName);
+  NS_ENSURE_ARG(aPrefName);
+
+  nsresult   rv = NS_NOINTERFACE;
+
+  // also check nsILocalFile, for backwards compatibility
+  if (aType.Equals(NS_GET_IID(nsIFile)) || aType.Equals(NS_GET_IID(nsILocalFile))) {
+    nsCOMPtr<nsIFile> file = do_QueryInterface(aValue);
+    if (!file)
+      return NS_NOINTERFACE;
+    nsAutoCString descriptorString;
+
+    rv = file->GetPersistentDescriptor(descriptorString);
+    if (NS_SUCCEEDED(rv)) {
+      rv = SetCharPrefInternal(aPrefName, descriptorString.get());
+    }
+    return rv;
+  }
+
+  if (aType.Equals(NS_GET_IID(nsIRelativeFilePref))) {
+    nsCOMPtr<nsIRelativeFilePref> relFilePref = do_QueryInterface(aValue);
+    if (!relFilePref)
+      return NS_NOINTERFACE;
+
+    nsCOMPtr<nsIFile> file;
+    relFilePref->GetFile(getter_AddRefs(file));
+    if (!file)
+      return NS_NOINTERFACE;
+    nsAutoCString relativeToKey;
+    (void) relFilePref->GetRelativeToKey(relativeToKey);
+
+    nsCOMPtr<nsIFile> relativeToFile;
+    nsCOMPtr<nsIProperties> directoryService(do_GetService(NS_DIRECTORY_SERVICE_CONTRACTID, &rv));
+    if (NS_FAILED(rv))
+      return rv;
+    rv = directoryService->Get(relativeToKey.get(), NS_GET_IID(nsIFile), getter_AddRefs(relativeToFile));
+    if (NS_FAILED(rv))
+      return rv;
+
+    nsAutoCString relDescriptor;
+    rv = file->GetRelativeDescriptor(relativeToFile, relDescriptor);
+    if (NS_FAILED(rv))
+      return rv;
+
+    nsAutoCString descriptorString;
+    descriptorString.Append('[');
+    descriptorString.Append(relativeToKey);
+    descriptorString.Append(']');
+    descriptorString.Append(relDescriptor);
+    return SetCharPrefInternal(aPrefName, descriptorString.get());
+  }
+
+  if (aType.Equals(NS_GET_IID(nsISupportsString))) {
+    nsCOMPtr<nsISupportsString> theString = do_QueryInterface(aValue);
+
+    if (theString) {
+      nsString wideString;
+
+      rv = theString->GetData(wideString);
+      if (NS_SUCCEEDED(rv)) {
+        // Check sanity of string length before any lengthy conversion
+        rv = CheckSanityOfStringLength(aPrefName, wideString);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+        rv = SetCharPrefInternal(aPrefName, NS_ConvertUTF16toUTF8(wideString).get());
+      }
+    }
+    return rv;
+  }
+
+  if (aType.Equals(NS_GET_IID(nsIPrefLocalizedString))) {
+    nsCOMPtr<nsIPrefLocalizedString> theString = do_QueryInterface(aValue);
+
+    if (theString) {
+      nsXPIDLString wideString;
+
+      rv = theString->GetData(getter_Copies(wideString));
+      if (NS_SUCCEEDED(rv)) {
+        // Check sanity of string length before any lengthy conversion
+        rv = CheckSanityOfStringLength(aPrefName, wideString);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+        rv = SetCharPrefInternal(aPrefName, NS_ConvertUTF16toUTF8(wideString).get());
+      }
+    }
+    return rv;
+  }
+
+  NS_WARNING("nsPrefBranch::SetComplexValue - Unsupported interface type");
+  return NS_NOINTERFACE;
+}
+
+NS_IMETHODIMP nsPrefBranch::ClearUserPref(const char *aPrefName)
+{
+  ENSURE_MAIN_PROCESS("Cannot ClearUserPref from content process:", aPrefName);
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_ClearUserPref(pref);
+}
+
+NS_IMETHODIMP nsPrefBranch::PrefHasUserValue(const char *aPrefName, bool *_retval)
+{
+  NS_ENSURE_ARG_POINTER(_retval);
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  *_retval = PREF_HasUserPref(pref);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsPrefBranch::LockPref(const char *aPrefName)
+{
+  ENSURE_MAIN_PROCESS("Cannot LockPref from content process:", aPrefName);
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_LockPref(pref, true);
+}
+
+NS_IMETHODIMP nsPrefBranch::PrefIsLocked(const char *aPrefName, bool *_retval)
+{
+  ENSURE_MAIN_PROCESS("Cannot check PrefIsLocked from content process:", aPrefName);
+  NS_ENSURE_ARG_POINTER(_retval);
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  *_retval = PREF_PrefIsLocked(pref);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsPrefBranch::UnlockPref(const char *aPrefName)
+{
+  ENSURE_MAIN_PROCESS("Cannot UnlockPref from content process:", aPrefName);
+  NS_ENSURE_ARG(aPrefName);
+  const char *pref = getPrefName(aPrefName);
+  return PREF_LockPref(pref, false);
+}
+
+NS_IMETHODIMP nsPrefBranch::ResetBranch(const char *aStartingAt)
+{
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP nsPrefBranch::DeleteBranch(const char *aStartingAt)
+{
+  ENSURE_MAIN_PROCESS("Cannot DeleteBranch from content process:", aStartingAt);
+  NS_ENSURE_ARG(aStartingAt);
+  const char *pref = getPrefName(aStartingAt);
+  return PREF_DeleteBranch(pref);
+}
+
+NS_IMETHODIMP nsPrefBranch::GetChildList(const char *aStartingAt, uint32_t *aCount, char ***aChildArray)
+{
+  char            **outArray;
+  int32_t         numPrefs;
+  int32_t         dwIndex;
+  AutoTArray<nsCString, 32> prefArray;
+
+  NS_ENSURE_ARG(aStartingAt);
+  NS_ENSURE_ARG_POINTER(aCount);
+  NS_ENSURE_ARG_POINTER(aChildArray);
+
+  *aChildArray = nullptr;
+  *aCount = 0;
+
+  // this will contain a list of all the pref name strings
+  // allocate on the stack for speed
+
+  const char* parent = getPrefName(aStartingAt);
+  size_t parentLen = strlen(parent);
+  for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
+    auto entry = static_cast<PrefHashEntry*>(iter.Get());
+    if (strncmp(entry->key, parent, parentLen) == 0) {
+      prefArray.AppendElement(entry->key);
+    }
+  }
+
+  // now that we've built up the list, run the callback on
+  // all the matching elements
+  numPrefs = prefArray.Length();
+
+  if (numPrefs) {
+    outArray = (char **)moz_xmalloc(numPrefs * sizeof(char *));
+    if (!outArray)
+      return NS_ERROR_OUT_OF_MEMORY;
+
+    for (dwIndex = 0; dwIndex < numPrefs; ++dwIndex) {
+      // we need to lop off mPrefRoot in case the user is planning to pass this
+      // back to us because if they do we are going to add mPrefRoot again.
+      const nsCString& element = prefArray[dwIndex];
+      outArray[dwIndex] = (char *)nsMemory::Clone(
+        element.get() + mPrefRootLength, element.Length() - mPrefRootLength + 1);
+
+      if (!outArray[dwIndex]) {
+        // we ran out of memory... this is annoying
+        NS_FREE_XPCOM_ALLOCATED_POINTER_ARRAY(dwIndex, outArray);
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+    }
+    *aChildArray = outArray;
+  }
+  *aCount = numPrefs;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsPrefBranch::AddObserver(const char *aDomain, nsIObserver *aObserver, bool aHoldWeak)
+{
+  PrefCallback *pCallback;
+  const char *pref;
+
+  NS_ENSURE_ARG(aDomain);
+  NS_ENSURE_ARG(aObserver);
+
+  // hold a weak reference to the observer if so requested
+  if (aHoldWeak) {
+    nsCOMPtr<nsISupportsWeakReference> weakRefFactory = do_QueryInterface(aObserver);
+    if (!weakRefFactory) {
+      // the caller didn't give us a object that supports weak reference... tell them
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    // Construct a PrefCallback with a weak reference to the observer.
+    pCallback = new PrefCallback(aDomain, weakRefFactory, this);
+
+  } else {
+    // Construct a PrefCallback with a strong reference to the observer.
+    pCallback = new PrefCallback(aDomain, aObserver, this);
+  }
+
+  if (mObservers.Get(pCallback)) {
+    NS_WARNING("Ignoring duplicate observer.");
+    delete pCallback;
+    return NS_OK;
+  }
+
+  mObservers.Put(pCallback, pCallback);
+
+  // We must pass a fully qualified preference name to the callback
+  // aDomain == nullptr is the only possible failure, and we trapped it with
+  // NS_ENSURE_ARG above.
+  pref = getPrefName(aDomain);
+  PREF_RegisterCallback(pref, NotifyObserver, pCallback);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsPrefBranch::RemoveObserver(const char *aDomain, nsIObserver *aObserver)
+{
+  NS_ENSURE_ARG(aDomain);
+  NS_ENSURE_ARG(aObserver);
+
+  nsresult rv = NS_OK;
+
+  // If we're in the middle of a call to freeObserverList, don't process this
+  // RemoveObserver call -- the observer in question will be removed soon, if
+  // it hasn't been already.
+  //
+  // It's important that we don't touch mObservers in any way -- even a Get()
+  // which returns null might cause the hashtable to resize itself, which will
+  // break the iteration in freeObserverList.
+  if (mFreeingObserverList)
+    return NS_OK;
+
+  // Remove the relevant PrefCallback from mObservers and get an owning
+  // pointer to it.  Unregister the callback first, and then let the owning
+  // pointer go out of scope and destroy the callback.
+  PrefCallback key(aDomain, aObserver, this);
+  nsAutoPtr<PrefCallback> pCallback;
+  mObservers.RemoveAndForget(&key, pCallback);
+  if (pCallback) {
+    // aDomain == nullptr is the only possible failure, trapped above
+    const char *pref = getPrefName(aDomain);
+    rv = PREF_UnregisterCallback(pref, NotifyObserver, pCallback);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP nsPrefBranch::Observe(nsISupports *aSubject, const char *aTopic, const char16_t *someData)
+{
+  // watch for xpcom shutdown and free our observers to eliminate any cyclic references
+  if (!nsCRT::strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID)) {
+    freeObserverList();
+  }
+  return NS_OK;
+}
+
+/* static */
+void nsPrefBranch::NotifyObserver(const char *newpref, void *data)
+{
+  PrefCallback *pCallback = (PrefCallback *)data;
+
+  nsCOMPtr<nsIObserver> observer = pCallback->GetObserver();
+  if (!observer) {
+    // The observer has expired.  Let's remove this callback.
+    pCallback->GetPrefBranch()->RemoveExpiredCallback(pCallback);
+    return;
+  }
+
+  // remove any root this string may contain so as to not confuse the observer
+  // by passing them something other than what they passed us as a topic
+  uint32_t len = pCallback->GetPrefBranch()->GetRootLength();
+  nsAutoCString suffix(newpref + len);
+
+  observer->Observe(static_cast<nsIPrefBranch *>(pCallback->GetPrefBranch()),
+                    NS_PREFBRANCH_PREFCHANGE_TOPIC_ID,
+                    NS_ConvertASCIItoUTF16(suffix).get());
+}
+
+size_t
+nsPrefBranch::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf)
+{
+  size_t n = aMallocSizeOf(this);
+  n += mPrefRoot.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+  n += mObservers.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  return n;
+}
+
+void nsPrefBranch::freeObserverList(void)
+{
+  // We need to prevent anyone from modifying mObservers while we're iterating
+  // over it. In particular, some clients will call RemoveObserver() when
+  // they're removed and destructed via the iterator; we set
+  // mFreeingObserverList to keep those calls from touching mObservers.
+  mFreeingObserverList = true;
+  for (auto iter = mObservers.Iter(); !iter.Done(); iter.Next()) {
+    nsAutoPtr<PrefCallback>& callback = iter.Data();
+    nsPrefBranch *prefBranch = callback->GetPrefBranch();
+    const char *pref = prefBranch->getPrefName(callback->GetDomain().get());
+    PREF_UnregisterCallback(pref, nsPrefBranch::NotifyObserver, callback);
+    iter.Remove();
+  }
+  mFreeingObserverList = false;
+}
+
+void
+nsPrefBranch::RemoveExpiredCallback(PrefCallback *aCallback)
+{
+  NS_PRECONDITION(aCallback->IsExpired(), "Callback should be expired.");
+  mObservers.Remove(aCallback);
+}
+
+nsresult nsPrefBranch::GetDefaultFromPropertiesFile(const char *aPrefName, char16_t **return_buf)
+{
+  nsresult rv;
+
+  // the default value contains a URL to a .properties file
+    
+  nsXPIDLCString propertyFileURL;
+  rv = PREF_CopyCharPref(aPrefName, getter_Copies(propertyFileURL), true);
+  if (NS_FAILED(rv))
+    return rv;
+
+  nsCOMPtr<nsIStringBundleService> bundleService =
+    mozilla::services::GetStringBundleService();
+  if (!bundleService)
+    return NS_ERROR_FAILURE;
+
+  nsCOMPtr<nsIStringBundle> bundle;
+  rv = bundleService->CreateBundle(propertyFileURL,
+                                   getter_AddRefs(bundle));
+  if (NS_FAILED(rv))
+    return rv;
+
+  // string names are in unicode
+  nsAutoString stringId;
+  stringId.AssignASCII(aPrefName);
+
+  return bundle->GetStringFromName(stringId.get(), return_buf);
+}
+
+const char *nsPrefBranch::getPrefName(const char *aPrefName)
+{
+  NS_ASSERTION(aPrefName, "null pref name!");
+
+  // for speed, avoid strcpy if we can:
+  if (mPrefRoot.IsEmpty())
+    return aPrefName;
+
+  // isn't there a better way to do this? this is really kind of gross.
+  mPrefRoot.Truncate(mPrefRootLength);
+  mPrefRoot.Append(aPrefName);
+  return mPrefRoot.get();
+}
+
+//----------------------------------------------------------------------------
+// nsPrefLocalizedString
+//----------------------------------------------------------------------------
+
+nsPrefLocalizedString::nsPrefLocalizedString()
+{
+}
+
+nsPrefLocalizedString::~nsPrefLocalizedString()
+{
+}
+
+
+/*
+ * nsISupports Implementation
+ */
+
+NS_IMPL_ADDREF(nsPrefLocalizedString)
+NS_IMPL_RELEASE(nsPrefLocalizedString)
+
+NS_INTERFACE_MAP_BEGIN(nsPrefLocalizedString)
+    NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIPrefLocalizedString)
+    NS_INTERFACE_MAP_ENTRY(nsIPrefLocalizedString)
+    NS_INTERFACE_MAP_ENTRY(nsISupportsString)
+NS_INTERFACE_MAP_END
+
+nsresult nsPrefLocalizedString::Init()
+{
+  nsresult rv;
+  mUnicodeString = do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID, &rv);
+
+  return rv;
+}
+
+NS_IMETHODIMP
+nsPrefLocalizedString::GetData(char16_t **_retval)
+{
+  nsAutoString data;
+
+  nsresult rv = GetData(data);
+  if (NS_FAILED(rv))
+    return rv;
+  
+  *_retval = ToNewUnicode(data);
+  if (!*_retval)
+    return NS_ERROR_OUT_OF_MEMORY;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsPrefLocalizedString::SetData(const char16_t *aData)
+{
+  if (!aData)
+    return SetData(EmptyString());
+  return SetData(nsDependentString(aData));
+}
+
+NS_IMETHODIMP
+nsPrefLocalizedString::SetDataWithLength(uint32_t aLength,
+                                         const char16_t *aData)
+{
+  if (!aData)
+    return SetData(EmptyString());
+  return SetData(Substring(aData, aLength));
+}
+
+//----------------------------------------------------------------------------
+// nsRelativeFilePref
+//----------------------------------------------------------------------------
+
+NS_IMPL_ISUPPORTS(nsRelativeFilePref, nsIRelativeFilePref)
+
+nsRelativeFilePref::nsRelativeFilePref()
+{
+}
+
+nsRelativeFilePref::~nsRelativeFilePref()
+{
+}
+
+NS_IMETHODIMP nsRelativeFilePref::GetFile(nsIFile **aFile)
+{
+  NS_ENSURE_ARG_POINTER(aFile);
+  *aFile = mFile;
+  NS_IF_ADDREF(*aFile);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsRelativeFilePref::SetFile(nsIFile *aFile)
+{
+  mFile = aFile;
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsRelativeFilePref::GetRelativeToKey(nsACString& aRelativeToKey)
+{
+  aRelativeToKey.Assign(mRelativeToKey);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsRelativeFilePref::SetRelativeToKey(const nsACString& aRelativeToKey)
+{
+  mRelativeToKey.Assign(aRelativeToKey);
+  return NS_OK;
+}
+
+#undef ENSURE_MAIN_PROCESS
diff --git a/components/preferences/src/nsPrefBranch.h b/components/preferences/src/nsPrefBranch.h
new file mode 100644
index 000000000..37cf5c2c4
--- /dev/null
+++ b/components/preferences/src/nsPrefBranch.h
@@ -0,0 +1,269 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsPrefBranch_h
+#define nsPrefBranch_h
+
+#include "nsCOMPtr.h"
+#include "nsIObserver.h"
+#include "nsIPrefBranch.h"
+#include "nsIPrefBranchInternal.h"
+#include "nsIPrefLocalizedString.h"
+#include "nsXPCOM.h"
+#include "nsISupportsPrimitives.h"
+#include "nsIRelativeFilePref.h"
+#include "nsIFile.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nsWeakReference.h"
+#include "nsClassHashtable.h"
+#include "nsCRT.h"
+#include "nsISupportsImpl.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/MemoryReporting.h"
+
+namespace mozilla {
+class PreferenceServiceReporter;
+} // namespace mozilla
+
+class nsPrefBranch;
+
+class PrefCallback : public PLDHashEntryHdr {
+  friend class mozilla::PreferenceServiceReporter;
+
+  public:
+    typedef PrefCallback* KeyType;
+    typedef const PrefCallback* KeyTypePointer;
+
+    static const PrefCallback* KeyToPointer(PrefCallback *aKey)
+    {
+      return aKey;
+    }
+
+    static PLDHashNumber HashKey(const PrefCallback *aKey)
+    {
+      uint32_t hash = mozilla::HashString(aKey->mDomain);
+      return mozilla::AddToHash(hash, aKey->mCanonical);
+    }
+
+
+  public:
+    // Create a PrefCallback with a strong reference to its observer.
+    PrefCallback(const char *aDomain, nsIObserver *aObserver,
+                 nsPrefBranch *aBranch)
+      : mDomain(aDomain),
+        mBranch(aBranch),
+        mWeakRef(nullptr),
+        mStrongRef(aObserver)
+    {
+      MOZ_COUNT_CTOR(PrefCallback);
+      nsCOMPtr<nsISupports> canonical = do_QueryInterface(aObserver);
+      mCanonical = canonical;
+    }
+
+    // Create a PrefCallback with a weak reference to its observer.
+    PrefCallback(const char *aDomain,
+                 nsISupportsWeakReference *aObserver,
+                 nsPrefBranch *aBranch)
+      : mDomain(aDomain),
+        mBranch(aBranch),
+        mWeakRef(do_GetWeakReference(aObserver)),
+        mStrongRef(nullptr)
+    {
+      MOZ_COUNT_CTOR(PrefCallback);
+      nsCOMPtr<nsISupports> canonical = do_QueryInterface(aObserver);
+      mCanonical = canonical;
+    }
+
+    // Copy constructor needs to be explicit or the linker complains.
+    explicit PrefCallback(const PrefCallback *&aCopy)
+      : mDomain(aCopy->mDomain),
+        mBranch(aCopy->mBranch),
+        mWeakRef(aCopy->mWeakRef),
+        mStrongRef(aCopy->mStrongRef),
+        mCanonical(aCopy->mCanonical)
+    {
+      MOZ_COUNT_CTOR(PrefCallback);
+    }
+
+    ~PrefCallback()
+    {
+      MOZ_COUNT_DTOR(PrefCallback);
+    }
+
+    bool KeyEquals(const PrefCallback *aKey) const
+    {
+      // We want to be able to look up a weakly-referencing PrefCallback after
+      // its observer has died so we can remove it from the table.  Once the
+      // callback's observer dies, its canonical pointer is stale -- in
+      // particular, we may have allocated a new observer in the same spot in
+      // memory!  So we can't just compare canonical pointers to determine
+      // whether aKey refers to the same observer as this.
+      //
+      // Our workaround is based on the way we use this hashtable: When we ask
+      // the hashtable to remove a PrefCallback whose weak reference has
+      // expired, we use as the key for removal the same object as was inserted
+      // into the hashtable.  Thus we can say that if one of the keys' weak
+      // references has expired, the two keys are equal iff they're the same
+      // object.
+
+      if (IsExpired() || aKey->IsExpired())
+        return this == aKey;
+
+      if (mCanonical != aKey->mCanonical)
+        return false;
+
+      return mDomain.Equals(aKey->mDomain);
+    }
+
+    PrefCallback *GetKey() const
+    {
+      return const_cast<PrefCallback*>(this);
+    }
+
+    // Get a reference to the callback's observer, or null if the observer was
+    // weakly referenced and has been destroyed.
+    already_AddRefed<nsIObserver> GetObserver() const
+    {
+      if (!IsWeak()) {
+        nsCOMPtr<nsIObserver> copy = mStrongRef;
+        return copy.forget();
+      }
+
+      nsCOMPtr<nsIObserver> observer = do_QueryReferent(mWeakRef);
+      return observer.forget();
+    }
+
+    const nsCString& GetDomain() const
+    {
+      return mDomain;
+    }
+
+    nsPrefBranch* GetPrefBranch() const
+    {
+      return mBranch;
+    }
+
+    // Has this callback's weak reference died?
+    bool IsExpired() const
+    {
+      if (!IsWeak())
+        return false;
+
+      nsCOMPtr<nsIObserver> observer(do_QueryReferent(mWeakRef));
+      return !observer;
+    }
+
+    enum { ALLOW_MEMMOVE = true };
+
+  private:
+    nsCString             mDomain;
+    nsPrefBranch         *mBranch;
+
+    // Exactly one of mWeakRef and mStrongRef should be non-null.
+    nsWeakPtr             mWeakRef;
+    nsCOMPtr<nsIObserver> mStrongRef;
+
+    // We need a canonical nsISupports pointer, per bug 578392.
+    nsISupports          *mCanonical;
+
+    bool IsWeak() const
+    {
+      return !!mWeakRef;
+    }
+};
+
+class nsPrefBranch final : public nsIPrefBranchInternal,
+                           public nsIObserver,
+                           public nsSupportsWeakReference
+{
+  friend class mozilla::PreferenceServiceReporter;
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIPREFBRANCH
+  NS_DECL_NSIPREFBRANCH2
+  NS_DECL_NSIOBSERVER
+
+  nsPrefBranch(const char *aPrefRoot, bool aDefaultBranch);
+
+  int32_t GetRootLength() { return mPrefRootLength; }
+
+  nsresult RemoveObserverFromMap(const char *aDomain, nsISupports *aObserver);
+
+  static void NotifyObserver(const char *newpref, void *data);
+
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf);
+
+  static void ReportToConsole(const nsAString& aMessage);
+
+protected:
+  virtual ~nsPrefBranch();
+
+  nsPrefBranch()    /* disallow use of this constructer */
+    : mPrefRootLength(0)
+    , mIsDefault(false)
+    , mFreeingObserverList(false)
+  {}
+
+  nsresult   GetDefaultFromPropertiesFile(const char *aPrefName, char16_t **return_buf);
+  // As SetCharPref, but without any check on the length of |aValue|
+  nsresult   SetCharPrefInternal(const char *aPrefName, const char *aValue);
+  // Reject strings that are more than 1Mb, warn if strings are more than 16kb
+  nsresult   CheckSanityOfStringLength(const char* aPrefName, const nsAString& aValue);
+  nsresult   CheckSanityOfStringLength(const char* aPrefName, const char* aValue);
+  nsresult   CheckSanityOfStringLength(const char* aPrefName, const uint32_t aLength);
+  void RemoveExpiredCallback(PrefCallback *aCallback);
+  const char *getPrefName(const char *aPrefName);
+  void       freeObserverList(void);
+
+private:
+  int32_t               mPrefRootLength;
+  nsCString             mPrefRoot;
+  bool                  mIsDefault;
+
+  bool                  mFreeingObserverList;
+  nsClassHashtable<PrefCallback, PrefCallback> mObservers;
+};
+
+
+class nsPrefLocalizedString final : public nsIPrefLocalizedString,
+                                    public nsISupportsString
+{
+public:
+  nsPrefLocalizedString();
+
+  NS_DECL_ISUPPORTS
+  NS_FORWARD_NSISUPPORTSSTRING(mUnicodeString->)
+  NS_FORWARD_NSISUPPORTSPRIMITIVE(mUnicodeString->)
+
+  nsresult Init();
+
+private:
+  virtual ~nsPrefLocalizedString();
+
+  NS_IMETHOD GetData(char16_t**) override;
+  NS_IMETHOD SetData(const char16_t* aData) override;
+  NS_IMETHOD SetDataWithLength(uint32_t aLength, const char16_t *aData) override;
+
+  nsCOMPtr<nsISupportsString> mUnicodeString;
+};
+
+
+class nsRelativeFilePref : public nsIRelativeFilePref
+{
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIRELATIVEFILEPREF
+
+  nsRelativeFilePref();
+
+private:
+  virtual ~nsRelativeFilePref();
+
+  nsCOMPtr<nsIFile> mFile;
+  nsCString mRelativeToKey;
+};
+
+#endif
diff --git a/components/preferences/src/nsPrefsFactory.cpp b/components/preferences/src/nsPrefsFactory.cpp
new file mode 100644
index 000000000..35a9885b9
--- /dev/null
+++ b/components/preferences/src/nsPrefsFactory.cpp
@@ -0,0 +1,54 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/ModuleUtils.h"
+#include "mozilla/Preferences.h"
+#include "nsPrefBranch.h"
+#include "prefapi.h"
+
+using namespace mozilla;
+
+NS_GENERIC_FACTORY_SINGLETON_CONSTRUCTOR(Preferences,
+                                         Preferences::GetInstanceForService)
+NS_GENERIC_FACTORY_CONSTRUCTOR_INIT(nsPrefLocalizedString, Init)
+NS_GENERIC_FACTORY_CONSTRUCTOR(nsRelativeFilePref)
+
+static NS_DEFINE_CID(kPrefServiceCID, NS_PREFSERVICE_CID);
+static NS_DEFINE_CID(kPrefLocalizedStringCID, NS_PREFLOCALIZEDSTRING_CID);
+static NS_DEFINE_CID(kRelativeFilePrefCID, NS_RELATIVEFILEPREF_CID);
+ 
+static mozilla::Module::CIDEntry kPrefCIDs[] = {
+  { &kPrefServiceCID, true, nullptr, PreferencesConstructor },
+  { &kPrefLocalizedStringCID, false, nullptr, nsPrefLocalizedStringConstructor },
+  { &kRelativeFilePrefCID, false, nullptr, nsRelativeFilePrefConstructor },
+  { nullptr }
+};
+
+static mozilla::Module::ContractIDEntry kPrefContracts[] = {
+  { NS_PREFSERVICE_CONTRACTID, &kPrefServiceCID },
+  { NS_PREFLOCALIZEDSTRING_CONTRACTID, &kPrefLocalizedStringCID },
+  { NS_RELATIVEFILEPREF_CONTRACTID, &kRelativeFilePrefCID },
+  // compatibility for extension that uses old service
+  { "@mozilla.org/preferences;1", &kPrefServiceCID },
+  { nullptr }
+};
+
+static void
+UnloadPrefsModule()
+{
+  Preferences::Shutdown();
+}
+
+static const mozilla::Module kPrefModule = {
+  mozilla::Module::kVersion,
+  kPrefCIDs,
+  kPrefContracts,
+  nullptr,
+  nullptr,
+  nullptr,
+  UnloadPrefsModule
+};
+
+NSMODULE_DEFN(nsPrefModule) = &kPrefModule;
diff --git a/components/preferences/src/prefapi.cpp b/components/preferences/src/prefapi.cpp
new file mode 100644
index 000000000..8aaf4077b
--- /dev/null
+++ b/components/preferences/src/prefapi.cpp
@@ -0,0 +1,1005 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+
+#include "prefapi.h"
+#include "prefapi_private_data.h"
+#include "prefread.h"
+#include "MainThreadUtils.h"
+#include "nsReadableUtils.h"
+#include "nsCRT.h"
+
+#define PL_ARENA_CONST_ALIGN_MASK 3
+#include "plarena.h"
+
+#ifdef _WIN32
+  #include "windows.h"
+#endif /* _WIN32 */
+
+#include "plstr.h"
+#include "PLDHashTable.h"
+#include "plbase64.h"
+#include "mozilla/Logging.h"
+#include "prprf.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/dom/PContent.h"
+#include "nsQuickSort.h"
+#include "nsString.h"
+#include "nsPrintfCString.h"
+#include "prlink.h"
+
+using namespace mozilla;
+
+static void
+clearPrefEntry(PLDHashTable *table, PLDHashEntryHdr *entry)
+{
+    PrefHashEntry *pref = static_cast<PrefHashEntry *>(entry);
+    if (pref->prefFlags.IsTypeString())
+    {
+        if (pref->defaultPref.stringVal)
+            PL_strfree(pref->defaultPref.stringVal);
+        if (pref->userPref.stringVal)
+            PL_strfree(pref->userPref.stringVal);
+    }
+    // don't need to free this as it's allocated in memory owned by
+    // gPrefNameArena
+    pref->key = nullptr;
+    memset(entry, 0, table->EntrySize());
+}
+
+static bool
+matchPrefEntry(const PLDHashEntryHdr* entry, const void* key)
+{
+    const PrefHashEntry *prefEntry =
+        static_cast<const PrefHashEntry*>(entry);
+
+    if (prefEntry->key == key) return true;
+
+    if (!prefEntry->key || !key) return false;
+
+    const char *otherKey = reinterpret_cast<const char*>(key);
+    return (strcmp(prefEntry->key, otherKey) == 0);
+}
+
+PLDHashTable*       gHashTable;
+static PLArenaPool  gPrefNameArena;
+
+static struct CallbackNode* gCallbacks = nullptr;
+static bool         gIsAnyPrefLocked = false;
+// These are only used during the call to pref_DoCallback
+static bool         gCallbacksInProgress = false;
+static bool         gShouldCleanupDeadNodes = false;
+
+
+static PLDHashTableOps     pref_HashTableOps = {
+    PLDHashTable::HashStringKey,
+    matchPrefEntry,
+    PLDHashTable::MoveEntryStub,
+    clearPrefEntry,
+    nullptr,
+};
+
+// PR_ALIGN_OF_WORD is only defined on some platforms.  ALIGN_OF_WORD has
+// already been defined to PR_ALIGN_OF_WORD everywhere
+#ifndef PR_ALIGN_OF_WORD
+#define PR_ALIGN_OF_WORD PR_ALIGN_OF_POINTER
+#endif
+
+// making PrefName arena 8k for nice allocation
+#define PREFNAME_ARENA_SIZE 8192
+
+#define WORD_ALIGN_MASK (PR_ALIGN_OF_WORD - 1)
+
+// sanity checking
+#if (PR_ALIGN_OF_WORD & WORD_ALIGN_MASK) != 0
+#error "PR_ALIGN_OF_WORD must be a power of 2!"
+#endif
+
+// equivalent to strdup() - does no error checking,
+// we're assuming we're only called with a valid pointer
+static char *ArenaStrDup(const char* str, PLArenaPool* aArena)
+{
+    void* mem;
+    uint32_t len = strlen(str);
+    PL_ARENA_ALLOCATE(mem, aArena, len+1);
+    if (mem)
+        memcpy(mem, str, len+1);
+    return static_cast<char*>(mem);
+}
+
+static PrefsDirtyFunc gDirtyCallback = nullptr;
+
+inline void MakeDirtyCallback()
+{
+    // Right now the callback function is always set, so we don't need
+    // to complicate the code to cover the scenario where we set the callback
+    // after we've already tried to make it dirty.  If this assert triggers
+    // we will add that code.
+    MOZ_ASSERT(gDirtyCallback);
+    if (gDirtyCallback) {
+        gDirtyCallback();
+    }
+}
+
+void PREF_SetDirtyCallback(PrefsDirtyFunc aFunc)
+{
+    gDirtyCallback = aFunc;
+}
+
+/*---------------------------------------------------------------------------*/
+
+static bool pref_ValueChanged(PrefValue oldValue, PrefValue newValue, PrefType type);
+/* -- Privates */
+struct CallbackNode {
+    char*                   domain;
+    // If someone attempts to remove the node from the callback list while
+    // pref_DoCallback is running, |func| is set to nullptr. Such nodes will
+    // be removed at the end of pref_DoCallback.
+    PrefChangedFunc         func;
+    void*                   data;
+    struct CallbackNode*    next;
+};
+
+/* -- Prototypes */
+static nsresult pref_DoCallback(const char* changed_pref);
+
+enum {
+    kPrefSetDefault = 1,
+    kPrefForceSet = 2,
+    kPrefStickyDefault = 4,
+};
+static nsresult pref_HashPref(const char *key, PrefValue value, PrefType type, uint32_t flags);
+
+#define PREF_HASHTABLE_INITIAL_LENGTH   1024
+
+void PREF_Init()
+{
+    if (!gHashTable) {
+        gHashTable = new PLDHashTable(&pref_HashTableOps,
+                                      sizeof(PrefHashEntry),
+                                      PREF_HASHTABLE_INITIAL_LENGTH);
+
+        PL_INIT_ARENA_POOL(&gPrefNameArena, "PrefNameArena",
+                           PREFNAME_ARENA_SIZE);
+    }
+}
+
+/* Frees the callback list. */
+void PREF_Cleanup()
+{
+    NS_ASSERTION(!gCallbacksInProgress,
+        "PREF_Cleanup was called while gCallbacksInProgress is true!");
+    struct CallbackNode* node = gCallbacks;
+    struct CallbackNode* next_node;
+
+    while (node)
+    {
+        next_node = node->next;
+        PL_strfree(node->domain);
+        free(node);
+        node = next_node;
+    }
+    gCallbacks = nullptr;
+
+    PREF_CleanupPrefs();
+}
+
+/* Frees up all the objects except the callback list. */
+void PREF_CleanupPrefs()
+{
+    if (gHashTable) {
+        delete gHashTable;
+        gHashTable = nullptr;
+        PL_FinishArenaPool(&gPrefNameArena);
+    }
+}
+
+// note that this appends to aResult, and does not assign!
+static void str_escape(const char * original, nsAFlatCString& aResult)
+{
+    /* JavaScript does not allow quotes, slashes, or line terminators inside
+     * strings so we must escape them. ECMAScript defines four line
+     * terminators, but we're only worrying about \r and \n here.  We currently
+     * feed our pref script to the JS interpreter as Latin-1 so  we won't
+     * encounter \u2028 (line separator) or \u2029 (paragraph separator).
+     *
+     * WARNING: There are hints that we may be moving to storing prefs
+     * as utf8. If we ever feed them to the JS compiler as UTF8 then
+     * we'll have to worry about the multibyte sequences that would be
+     * interpreted as \u2028 and \u2029
+     */
+    const char *p;
+
+    if (original == nullptr)
+        return;
+
+    /* Paranoid worst case all slashes will free quickly */
+    for  (p=original; *p; ++p)
+    {
+        switch (*p)
+        {
+            case '\n':
+                aResult.AppendLiteral("\\n");
+                break;
+
+            case '\r':
+                aResult.AppendLiteral("\\r");
+                break;
+
+            case '\\':
+                aResult.AppendLiteral("\\\\");
+                break;
+
+            case '\"':
+                aResult.AppendLiteral("\\\"");
+                break;
+
+            default:
+                aResult.Append(*p);
+                break;
+        }
+    }
+}
+
+/*
+** External calls
+*/
+nsresult
+PREF_SetCharPref(const char *pref_name, const char *value, bool set_default)
+{
+    if ((uint32_t)strlen(value) > MAX_PREF_LENGTH) {
+        return NS_ERROR_ILLEGAL_VALUE;
+    }
+
+    PrefValue pref;
+    pref.stringVal = (char*)value;
+
+    return pref_HashPref(pref_name, pref, PrefType::String, set_default ? kPrefSetDefault : 0);
+}
+
+nsresult
+PREF_SetIntPref(const char *pref_name, int32_t value, bool set_default)
+{
+    PrefValue pref;
+    pref.intVal = value;
+
+    return pref_HashPref(pref_name, pref, PrefType::Int, set_default ? kPrefSetDefault : 0);
+}
+
+nsresult
+PREF_SetBoolPref(const char *pref_name, bool value, bool set_default)
+{
+    PrefValue pref;
+    pref.boolVal = value;
+
+    return pref_HashPref(pref_name, pref, PrefType::Bool, set_default ? kPrefSetDefault : 0);
+}
+
+enum WhichValue { DEFAULT_VALUE, USER_VALUE };
+static nsresult
+SetPrefValue(const char* aPrefName, const dom::PrefValue& aValue,
+             WhichValue aWhich)
+{
+    bool setDefault = (aWhich == DEFAULT_VALUE);
+    switch (aValue.type()) {
+    case dom::PrefValue::TnsCString:
+        return PREF_SetCharPref(aPrefName, aValue.get_nsCString().get(),
+                                setDefault);
+    case dom::PrefValue::Tint32_t:
+        return PREF_SetIntPref(aPrefName, aValue.get_int32_t(),
+                               setDefault);
+    case dom::PrefValue::Tbool:
+        return PREF_SetBoolPref(aPrefName, aValue.get_bool(),
+                                setDefault);
+    default:
+        MOZ_CRASH();
+    }
+}
+
+nsresult
+pref_SetPref(const dom::PrefSetting& aPref)
+{
+    const char* prefName = aPref.name().get();
+    const dom::MaybePrefValue& defaultValue = aPref.defaultValue();
+    const dom::MaybePrefValue& userValue = aPref.userValue();
+
+    nsresult rv;
+    if (defaultValue.type() == dom::MaybePrefValue::TPrefValue) {
+        rv = SetPrefValue(prefName, defaultValue.get_PrefValue(), DEFAULT_VALUE);
+        if (NS_FAILED(rv)) {
+            return rv;
+        }
+    }
+
+    if (userValue.type() == dom::MaybePrefValue::TPrefValue) {
+        rv = SetPrefValue(prefName, userValue.get_PrefValue(), USER_VALUE);
+    } else {
+        rv = PREF_ClearUserPref(prefName);
+    }
+
+    // NB: we should never try to clear a default value, that doesn't
+    // make sense
+
+    return rv;
+}
+
+UniquePtr<char*[]>
+pref_savePrefs(PLDHashTable* aTable, uint32_t* aPrefCount)
+{
+    // This function allocates the entries in the savedPrefs array it returns.
+    // It is the callers responsibility to go through the array and free
+    // all of them.  The aPrefCount entries will be non-null.  Any end padding
+    // is an implementation detail and may change.
+    MOZ_ASSERT(aPrefCount);
+    auto savedPrefs = MakeUnique<char*[]>(aTable->EntryCount());
+
+    // This is not necessary, but leaving it in for now
+    memset(savedPrefs.get(), 0, aTable->EntryCount() * sizeof(char*));
+
+    int32_t j = 0;
+    for (auto iter = aTable->Iter(); !iter.Done(); iter.Next()) {
+        auto pref = static_cast<PrefHashEntry*>(iter.Get());
+
+        nsAutoCString prefValue;
+        nsAutoCString prefPrefix;
+        prefPrefix.AssignLiteral("user_pref(\"");
+
+        // where we're getting our pref from
+        PrefValue* sourcePref;
+
+        if (pref->prefFlags.HasUserValue() &&
+            (pref_ValueChanged(pref->defaultPref,
+                               pref->userPref,
+                               pref->prefFlags.GetPrefType()) ||
+             !(pref->prefFlags.HasDefault()) ||
+             pref->prefFlags.HasStickyDefault())) {
+            sourcePref = &pref->userPref;
+        } else {
+            // do not save default prefs that haven't changed
+            continue;
+        }
+
+        // strings are in quotes!
+        if (pref->prefFlags.IsTypeString()) {
+            prefValue = '\"';
+            str_escape(sourcePref->stringVal, prefValue);
+            prefValue += '\"';
+
+        } else if (pref->prefFlags.IsTypeInt()) {
+            prefValue.AppendInt(sourcePref->intVal);
+
+        } else if (pref->prefFlags.IsTypeBool()) {
+            prefValue = (sourcePref->boolVal) ? "true" : "false";
+        }
+
+        nsAutoCString prefName;
+        str_escape(pref->key, prefName);
+
+        savedPrefs[j++] = ToNewCString(prefPrefix +
+                                       prefName +
+                                       NS_LITERAL_CSTRING("\", ") +
+                                       prefValue +
+                                       NS_LITERAL_CSTRING(");"));
+    }
+    *aPrefCount = j;
+
+    return savedPrefs;
+}
+
+bool
+pref_EntryHasAdvisablySizedValues(PrefHashEntry* aHashEntry)
+{
+    if (aHashEntry->prefFlags.GetPrefType() != PrefType::String) {
+        return true;
+    }
+
+    char* stringVal;
+    if (aHashEntry->prefFlags.HasDefault()) {
+        stringVal = aHashEntry->defaultPref.stringVal;
+        if (strlen(stringVal) > MAX_ADVISABLE_PREF_LENGTH) {
+            return false;
+        }
+    }
+
+    if (aHashEntry->prefFlags.HasUserValue()) {
+        stringVal = aHashEntry->userPref.stringVal;
+        if (strlen(stringVal) > MAX_ADVISABLE_PREF_LENGTH) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+static void
+GetPrefValueFromEntry(PrefHashEntry *aHashEntry, dom::PrefSetting* aPref,
+                      WhichValue aWhich)
+{
+    PrefValue* value;
+    dom::PrefValue* settingValue;
+    if (aWhich == USER_VALUE) {
+        value = &aHashEntry->userPref;
+        aPref->userValue() = dom::PrefValue();
+        settingValue = &aPref->userValue().get_PrefValue();
+    } else {
+        value = &aHashEntry->defaultPref;
+        aPref->defaultValue() = dom::PrefValue();
+        settingValue = &aPref->defaultValue().get_PrefValue();
+    }
+
+    switch (aHashEntry->prefFlags.GetPrefType()) {
+      case PrefType::String:
+        *settingValue = nsDependentCString(value->stringVal);
+        return;
+      case PrefType::Int:
+        *settingValue = value->intVal;
+        return;
+      case PrefType::Bool:
+        *settingValue = !!value->boolVal;
+        return;
+    default:
+        MOZ_CRASH();
+    }
+}
+
+void
+pref_GetPrefFromEntry(PrefHashEntry *aHashEntry, dom::PrefSetting* aPref)
+{
+    aPref->name() = aHashEntry->key;
+    if (aHashEntry->prefFlags.HasDefault()) {
+        GetPrefValueFromEntry(aHashEntry, aPref, DEFAULT_VALUE);
+    } else {
+        aPref->defaultValue() = null_t();
+    }
+    if (aHashEntry->prefFlags.HasUserValue()) {
+        GetPrefValueFromEntry(aHashEntry, aPref, USER_VALUE);
+    } else {
+        aPref->userValue() = null_t();
+    }
+
+    MOZ_ASSERT(aPref->defaultValue().type() == dom::MaybePrefValue::Tnull_t ||
+               aPref->userValue().type() == dom::MaybePrefValue::Tnull_t ||
+               (aPref->defaultValue().get_PrefValue().type() ==
+                aPref->userValue().get_PrefValue().type()));
+}
+
+
+int
+pref_CompareStrings(const void *v1, const void *v2, void *unused)
+{
+    char *s1 = *(char**) v1;
+    char *s2 = *(char**) v2;
+
+    if (!s1)
+    {
+        if (!s2)
+            return 0;
+        else
+            return -1;
+    }
+    else if (!s2)
+        return 1;
+    else
+        return strcmp(s1, s2);
+}
+
+bool PREF_HasUserPref(const char *pref_name)
+{
+    if (!gHashTable)
+        return false;
+
+    PrefHashEntry *pref = pref_HashTableLookup(pref_name);
+    return pref && pref->prefFlags.HasUserValue();
+}
+
+nsresult
+PREF_CopyCharPref(const char *pref_name, char ** return_buffer, bool get_default)
+{
+    if (!gHashTable)
+        return NS_ERROR_NOT_INITIALIZED;
+
+    nsresult rv = NS_ERROR_UNEXPECTED;
+    char* stringVal;
+    PrefHashEntry* pref = pref_HashTableLookup(pref_name);
+
+    if (pref && (pref->prefFlags.IsTypeString())) {
+        if (get_default || pref->prefFlags.IsLocked() || !pref->prefFlags.HasUserValue()) {
+            stringVal = pref->defaultPref.stringVal;
+        } else {
+            stringVal = pref->userPref.stringVal;
+        }
+
+        if (stringVal) {
+            *return_buffer = NS_strdup(stringVal);
+            rv = NS_OK;
+        }
+    }
+    return rv;
+}
+
+nsresult PREF_GetIntPref(const char *pref_name,int32_t * return_int, bool get_default)
+{
+    if (!gHashTable)
+        return NS_ERROR_NOT_INITIALIZED;
+
+    nsresult rv = NS_ERROR_UNEXPECTED;
+    PrefHashEntry* pref = pref_HashTableLookup(pref_name);
+    if (pref && (pref->prefFlags.IsTypeInt())) {
+        if (get_default || pref->prefFlags.IsLocked() || !pref->prefFlags.HasUserValue()) {
+            int32_t tempInt = pref->defaultPref.intVal;
+            /* check to see if we even had a default */
+            if (!pref->prefFlags.HasDefault()) {
+                return NS_ERROR_UNEXPECTED;
+            }
+            *return_int = tempInt;
+        } else {
+            *return_int = pref->userPref.intVal;
+        }
+        rv = NS_OK;
+    }
+    return rv;
+}
+
+nsresult PREF_GetBoolPref(const char *pref_name, bool * return_value, bool get_default)
+{
+    if (!gHashTable)
+        return NS_ERROR_NOT_INITIALIZED;
+
+    nsresult rv = NS_ERROR_UNEXPECTED;
+    PrefHashEntry* pref = pref_HashTableLookup(pref_name);
+    //NS_ASSERTION(pref, pref_name);
+    if (pref && (pref->prefFlags.IsTypeBool())) {
+        if (get_default || pref->prefFlags.IsLocked() || !pref->prefFlags.HasUserValue()) {
+            bool tempBool = pref->defaultPref.boolVal;
+            /* check to see if we even had a default */
+            if (pref->prefFlags.HasDefault()) {
+                *return_value = tempBool;
+                rv = NS_OK;
+            }
+        } else {
+            *return_value = pref->userPref.boolVal;
+            rv = NS_OK;
+        }
+    }
+    return rv;
+}
+
+nsresult
+PREF_DeleteBranch(const char *branch_name)
+{
+    MOZ_ASSERT(NS_IsMainThread());
+
+    int len = (int)strlen(branch_name);
+
+    if (!gHashTable)
+        return NS_ERROR_NOT_INITIALIZED;
+
+    /* The following check insures that if the branch name already has a "."
+     * at the end, we don't end up with a "..". This fixes an incompatibility
+     * between nsIPref, which needs the period added, and nsIPrefBranch which
+     * does not. When nsIPref goes away this function should be fixed to
+     * never add the period at all.
+     */
+    nsAutoCString branch_dot(branch_name);
+    if ((len > 1) && branch_name[len - 1] != '.')
+        branch_dot += '.';
+
+    /* Delete a branch. Used for deleting mime types */
+    const char *to_delete = branch_dot.get();
+    MOZ_ASSERT(to_delete);
+    len = strlen(to_delete);
+    for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
+        auto entry = static_cast<PrefHashEntry*>(iter.Get());
+
+        /* note if we're deleting "ldap" then we want to delete "ldap.xxx"
+            and "ldap" (if such a leaf node exists) but not "ldap_1.xxx" */
+        if (PL_strncmp(entry->key, to_delete, (uint32_t) len) == 0 ||
+            (len-1 == (int)strlen(entry->key) &&
+             PL_strncmp(entry->key, to_delete, (uint32_t)(len-1)) == 0)) {
+            iter.Remove();
+        }
+    }
+
+    MakeDirtyCallback();
+    return NS_OK;
+}
+
+
+nsresult
+PREF_ClearUserPref(const char *pref_name)
+{
+    if (!gHashTable)
+        return NS_ERROR_NOT_INITIALIZED;
+
+    PrefHashEntry* pref = pref_HashTableLookup(pref_name);
+    if (pref && pref->prefFlags.HasUserValue()) {
+        pref->prefFlags.SetHasUserValue(false);
+
+        if (!pref->prefFlags.HasDefault()) {
+            gHashTable->RemoveEntry(pref);
+        }
+
+        pref_DoCallback(pref_name);
+        MakeDirtyCallback();
+    }
+    return NS_OK;
+}
+
+nsresult
+PREF_ClearAllUserPrefs()
+{
+    MOZ_ASSERT(NS_IsMainThread());
+
+    if (!gHashTable)
+        return NS_ERROR_NOT_INITIALIZED;
+
+    std::vector<std::string> prefStrings;
+    for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
+        auto pref = static_cast<PrefHashEntry*>(iter.Get());
+
+        if (pref->prefFlags.HasUserValue()) {
+            prefStrings.push_back(std::string(pref->key));
+
+            pref->prefFlags.SetHasUserValue(false);
+            if (!pref->prefFlags.HasDefault()) {
+                iter.Remove();
+            }
+        }
+    }
+
+    for (std::string& prefString : prefStrings) {
+        pref_DoCallback(prefString.c_str());
+    }
+
+    MakeDirtyCallback();
+    return NS_OK;
+}
+
+nsresult PREF_LockPref(const char *key, bool lockit)
+{
+    if (!gHashTable)
+        return NS_ERROR_NOT_INITIALIZED;
+
+    PrefHashEntry* pref = pref_HashTableLookup(key);
+    if (!pref)
+        return NS_ERROR_UNEXPECTED;
+
+    if (lockit) {
+        if (!pref->prefFlags.IsLocked()) {
+            pref->prefFlags.SetLocked(true);
+            gIsAnyPrefLocked = true;
+            pref_DoCallback(key);
+        }
+    } else {
+        if (pref->prefFlags.IsLocked()) {
+            pref->prefFlags.SetLocked(false);
+            pref_DoCallback(key);
+        }
+    }
+    return NS_OK;
+}
+
+/*
+ * Hash table functions
+ */
+static bool pref_ValueChanged(PrefValue oldValue, PrefValue newValue, PrefType type)
+{
+    bool changed = true;
+    switch(type) {
+      case PrefType::String:
+        if (oldValue.stringVal && newValue.stringVal) {
+            changed = (strcmp(oldValue.stringVal, newValue.stringVal) != 0);
+        }
+        break;
+      case PrefType::Int:
+        changed = oldValue.intVal != newValue.intVal;
+        break;
+      case PrefType::Bool:
+        changed = oldValue.boolVal != newValue.boolVal;
+        break;
+      case PrefType::Invalid:
+      default:
+        changed = false;
+        break;
+    }
+    return changed;
+}
+
+/*
+ * Overwrite the type and value of an existing preference. Caller must
+ * ensure that they are not changing the type of a preference that has
+ * a default value.
+ */
+static PrefTypeFlags pref_SetValue(PrefValue* existingValue, PrefTypeFlags flags,
+                                   PrefValue newValue, PrefType newType)
+{
+    if (flags.IsTypeString() && existingValue->stringVal) {
+        PL_strfree(existingValue->stringVal);
+    }
+    flags.SetPrefType(newType);
+    if (flags.IsTypeString()) {
+        MOZ_ASSERT(newValue.stringVal);
+        existingValue->stringVal = newValue.stringVal ? PL_strdup(newValue.stringVal) : nullptr;
+    }
+    else {
+        *existingValue = newValue;
+    }
+    return flags;
+}
+
+PrefHashEntry* pref_HashTableLookup(const char *key)
+{
+    MOZ_ASSERT(NS_IsMainThread());
+
+    return static_cast<PrefHashEntry*>(gHashTable->Search(key));
+}
+
+nsresult pref_HashPref(const char *key, PrefValue value, PrefType type, uint32_t flags)
+{
+    MOZ_ASSERT(NS_IsMainThread());
+
+    if (!gHashTable)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    auto pref = static_cast<PrefHashEntry*>(gHashTable->Add(key, fallible));
+    if (!pref)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    // new entry, better initialize
+    if (!pref->key) {
+
+        // initialize the pref entry
+        pref->prefFlags.Reset().SetPrefType(type);
+        pref->key = ArenaStrDup(key, &gPrefNameArena);
+        memset(&pref->defaultPref, 0, sizeof(pref->defaultPref));
+        memset(&pref->userPref, 0, sizeof(pref->userPref));
+    } else if (pref->prefFlags.HasDefault() && !pref->prefFlags.IsPrefType(type)) {
+        NS_WARNING(nsPrintfCString("Trying to overwrite value of default pref %s with the wrong type!", key).get());
+        return NS_ERROR_UNEXPECTED;
+    }
+
+    bool valueChanged = false;
+    if (flags & kPrefSetDefault) {
+        if (!pref->prefFlags.IsLocked()) {
+            /* ?? change of semantics? */
+            if (pref_ValueChanged(pref->defaultPref, value, type) ||
+                !pref->prefFlags.HasDefault()) {
+                pref->prefFlags = pref_SetValue(&pref->defaultPref, pref->prefFlags, value, type).SetHasDefault(true);
+                if (flags & kPrefStickyDefault) {
+                    pref->prefFlags.SetHasStickyDefault(true);
+                }
+                if (!pref->prefFlags.HasUserValue()) {
+                    valueChanged = true;
+                }
+            }
+            // What if we change the default to be the same as the user value?
+            // Should we clear the user value?
+        }
+    } else {
+        /* If new value is same as the default value and it's not a "sticky"
+           pref, then un-set the user value.
+           Otherwise, set the user value only if it has changed */
+        if ((pref->prefFlags.HasDefault()) &&
+            !(pref->prefFlags.HasStickyDefault()) &&
+            !pref_ValueChanged(pref->defaultPref, value, type) &&
+            !(flags & kPrefForceSet)) {
+            if (pref->prefFlags.HasUserValue()) {
+                /* XXX should we free a user-set string value if there is one? */
+                pref->prefFlags.SetHasUserValue(false);
+                if (!pref->prefFlags.IsLocked()) {
+                    MakeDirtyCallback();
+                    valueChanged = true;
+                }
+            }
+        } else if (!pref->prefFlags.HasUserValue() ||
+                 !pref->prefFlags.IsPrefType(type) ||
+                 pref_ValueChanged(pref->userPref, value, type) ) {
+            pref->prefFlags = pref_SetValue(&pref->userPref, pref->prefFlags, value, type).SetHasUserValue(true);
+            if (!pref->prefFlags.IsLocked()) {
+                MakeDirtyCallback();
+                valueChanged = true;
+            }
+        }
+    }
+
+    if (valueChanged) {
+        return pref_DoCallback(key);
+    }
+    return NS_OK;
+}
+
+size_t
+pref_SizeOfPrivateData(MallocSizeOf aMallocSizeOf)
+{
+    size_t n = PL_SizeOfArenaPoolExcludingPool(&gPrefNameArena, aMallocSizeOf);
+    for (struct CallbackNode* node = gCallbacks; node; node = node->next) {
+        n += aMallocSizeOf(node);
+        n += aMallocSizeOf(node->domain);
+    }
+    return n;
+}
+
+PrefType
+PREF_GetPrefType(const char *pref_name)
+{
+    if (gHashTable) {
+        PrefHashEntry* pref = pref_HashTableLookup(pref_name);
+        if (pref) {
+            return pref->prefFlags.GetPrefType();
+        }
+    }
+    return PrefType::Invalid;
+}
+
+/* -- */
+
+bool
+PREF_PrefIsLocked(const char *pref_name)
+{
+    bool result = false;
+    if (gIsAnyPrefLocked && gHashTable) {
+        PrefHashEntry* pref = pref_HashTableLookup(pref_name);
+        if (pref && pref->prefFlags.IsLocked()) {
+            result = true;
+        }
+    }
+
+    return result;
+}
+
+/* Adds a node to the beginning of the callback list. */
+void
+PREF_RegisterCallback(const char *pref_node,
+                       PrefChangedFunc callback,
+                       void * instance_data)
+{
+    NS_PRECONDITION(pref_node, "pref_node must not be nullptr");
+    NS_PRECONDITION(callback, "callback must not be nullptr");
+
+    struct CallbackNode* node = (struct CallbackNode*) malloc(sizeof(struct CallbackNode));
+    if (node)
+    {
+        node->domain = PL_strdup(pref_node);
+        node->func = callback;
+        node->data = instance_data;
+        node->next = gCallbacks;
+        gCallbacks = node;
+    }
+    return;
+}
+
+/* Removes |node| from gCallbacks list.
+   Returns the node after the deleted one. */
+struct CallbackNode*
+pref_RemoveCallbackNode(struct CallbackNode* node,
+                        struct CallbackNode* prev_node)
+{
+    NS_PRECONDITION(!prev_node || prev_node->next == node, "invalid params");
+    NS_PRECONDITION(prev_node || gCallbacks == node, "invalid params");
+
+    NS_ASSERTION(!gCallbacksInProgress,
+        "modifying the callback list while gCallbacksInProgress is true");
+
+    struct CallbackNode* next_node = node->next;
+    if (prev_node)
+        prev_node->next = next_node;
+    else
+        gCallbacks = next_node;
+    PL_strfree(node->domain);
+    free(node);
+    return next_node;
+}
+
+/* Deletes a node from the callback list or marks it for deletion. */
+nsresult
+PREF_UnregisterCallback(const char *pref_node,
+                         PrefChangedFunc callback,
+                         void * instance_data)
+{
+    nsresult rv = NS_ERROR_FAILURE;
+    struct CallbackNode* node = gCallbacks;
+    struct CallbackNode* prev_node = nullptr;
+
+    while (node != nullptr)
+    {
+        if ( node->func == callback &&
+             node->data == instance_data &&
+             strcmp(node->domain, pref_node) == 0)
+        {
+            if (gCallbacksInProgress)
+            {
+                // postpone the node removal until after
+                // gCallbacks enumeration is finished.
+                node->func = nullptr;
+                gShouldCleanupDeadNodes = true;
+                prev_node = node;
+                node = node->next;
+            }
+            else
+            {
+                node = pref_RemoveCallbackNode(node, prev_node);
+            }
+            rv = NS_OK;
+        }
+        else
+        {
+            prev_node = node;
+            node = node->next;
+        }
+    }
+    return rv;
+}
+
+static nsresult pref_DoCallback(const char* changed_pref)
+{
+    nsresult rv = NS_OK;
+    struct CallbackNode* node;
+
+    bool reentered = gCallbacksInProgress;
+    gCallbacksInProgress = true;
+    // Nodes must not be deleted while gCallbacksInProgress is true.
+    // Nodes that need to be deleted are marked for deletion by nulling
+    // out the |func| pointer. We release them at the end of this function
+    // if we haven't reentered.
+
+    for (node = gCallbacks; node != nullptr; node = node->next)
+    {
+        if ( node->func &&
+             PL_strncmp(changed_pref,
+                        node->domain,
+                        strlen(node->domain)) == 0 )
+        {
+            (*node->func) (changed_pref, node->data);
+        }
+    }
+
+    gCallbacksInProgress = reentered;
+
+    if (gShouldCleanupDeadNodes && !gCallbacksInProgress)
+    {
+        struct CallbackNode* prev_node = nullptr;
+        node = gCallbacks;
+
+        while (node != nullptr)
+        {
+            if (!node->func)
+            {
+                node = pref_RemoveCallbackNode(node, prev_node);
+            }
+            else
+            {
+                prev_node = node;
+                node = node->next;
+            }
+        }
+        gShouldCleanupDeadNodes = false;
+    }
+
+    return rv;
+}
+
+void PREF_ReaderCallback(void       *closure,
+                         const char *pref,
+                         PrefValue   value,
+                         PrefType    type,
+                         bool        isDefault,
+                         bool        isStickyDefault)
+
+{
+    uint32_t flags = 0;
+    if (isDefault) {
+        flags |= kPrefSetDefault;
+        if (isStickyDefault) {
+            flags |= kPrefStickyDefault;
+        }
+    } else {
+        flags |= kPrefForceSet;
+    }
+    pref_HashPref(pref, value, type, flags);
+}
diff --git a/components/preferences/src/prefapi.h b/components/preferences/src/prefapi.h
new file mode 100644
index 000000000..9ef014ada
--- /dev/null
+++ b/components/preferences/src/prefapi.h
@@ -0,0 +1,258 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+// <pre>
+*/
+#ifndef PREFAPI_H
+#define PREFAPI_H
+
+#include "nscore.h"
+#include "PLDHashTable.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// 1 MB should be enough for everyone.
+static const uint32_t MAX_PREF_LENGTH = 1 * 1024 * 1024;
+// Actually, 4kb should be enough for everyone.
+static const uint32_t MAX_ADVISABLE_PREF_LENGTH = 4 * 1024;
+
+typedef union
+{
+    char*       stringVal;
+    int32_t     intVal;
+    bool        boolVal;
+} PrefValue;
+
+/*
+// <font color=blue>
+// The Init function initializes the preference context and creates
+// the preference hashtable.
+// </font>
+*/
+void        PREF_Init();
+
+/*
+// Cleanup should be called at program exit to free the
+// list of registered callbacks.
+*/
+void        PREF_Cleanup();
+void        PREF_CleanupPrefs();
+
+/*
+// <font color=blue>
+// Preference flags, including the native type of the preference. Changing any of these
+// values will require modifying the code inside of PrefTypeFlags class.
+// </font>
+*/
+
+enum class PrefType {
+  Invalid = 0,
+  String = 1,
+  Int = 2,
+  Bool = 3,
+};
+
+// Keep the type of the preference, as well as the flags guiding its behaviour.
+class PrefTypeFlags
+{
+public:
+  PrefTypeFlags() : mValue(AsInt(PrefType::Invalid)) {}
+  explicit PrefTypeFlags(PrefType aType) : mValue(AsInt(aType)) {}
+  PrefTypeFlags& Reset() { mValue = AsInt(PrefType::Invalid); return *this; }
+
+  bool IsTypeValid() const { return !IsPrefType(PrefType::Invalid); }
+  bool IsTypeString() const { return IsPrefType(PrefType::String); }
+  bool IsTypeInt() const { return IsPrefType(PrefType::Int); }
+  bool IsTypeBool() const { return IsPrefType(PrefType::Bool); }
+  bool IsPrefType(PrefType type) const { return GetPrefType() == type; }
+
+  PrefTypeFlags& SetPrefType(PrefType aType) {
+    mValue = mValue - AsInt(GetPrefType()) + AsInt(aType);
+    return *this;
+  }
+  PrefType GetPrefType() const {
+    return (PrefType)(mValue & (AsInt(PrefType::String) |
+                                AsInt(PrefType::Int) |
+                                AsInt(PrefType::Bool)));
+  }
+
+  bool HasDefault() const { return mValue & PREF_FLAG_HAS_DEFAULT; }
+  PrefTypeFlags& SetHasDefault(bool aSetOrUnset) { return SetFlag(PREF_FLAG_HAS_DEFAULT, aSetOrUnset); }
+
+  bool HasStickyDefault() const { return mValue & PREF_FLAG_STICKY_DEFAULT; }
+  PrefTypeFlags& SetHasStickyDefault(bool aSetOrUnset) { return SetFlag(PREF_FLAG_STICKY_DEFAULT, aSetOrUnset); }
+
+  bool IsLocked() const { return mValue & PREF_FLAG_LOCKED; }
+  PrefTypeFlags& SetLocked(bool aSetOrUnset) { return SetFlag(PREF_FLAG_LOCKED, aSetOrUnset); }
+
+  bool HasUserValue() const { return mValue & PREF_FLAG_USERSET; }
+  PrefTypeFlags& SetHasUserValue(bool aSetOrUnset) { return SetFlag(PREF_FLAG_USERSET, aSetOrUnset); }
+
+private:
+  static uint16_t AsInt(PrefType aType) { return (uint16_t)aType; }
+
+  PrefTypeFlags& SetFlag(uint16_t aFlag, bool aSetOrUnset) {
+    mValue = aSetOrUnset ? mValue | aFlag : mValue & ~aFlag;
+    return *this;
+  }
+
+  // Pack both the value of type (PrefType) and flags into the same int.  This is why
+  // the flag enum starts at 4, as PrefType occupies the bottom two bits.
+  enum {
+    PREF_FLAG_LOCKED = 4,
+    PREF_FLAG_USERSET = 8,
+    PREF_FLAG_CONFIG = 16,
+    PREF_FLAG_REMOTE = 32,
+    PREF_FLAG_LILOCAL = 64,
+    PREF_FLAG_HAS_DEFAULT = 128,
+    PREF_FLAG_STICKY_DEFAULT = 256,
+  };
+  uint16_t mValue;
+};
+
+struct PrefHashEntry : PLDHashEntryHdr
+{
+    PrefTypeFlags prefFlags; // This field goes first to minimize struct size on 64-bit.
+    const char *key;
+    PrefValue defaultPref;
+    PrefValue userPref;
+};
+
+/*
+// <font color=blue>
+// Set the various types of preferences.  These functions take a dotted
+// notation of the preference name (e.g. "browser.startup.homepage").
+// Note that this will cause the preference to be saved to the file if
+// it is different from the default.  In other words, these are used
+// to set the _user_ preferences.
+//
+// If set_default is set to true however, it sets the default value.
+// This will only affect the program behavior if the user does not have a value
+// saved over it for the particular preference.  In addition, these will never
+// be saved out to disk.
+//
+// Each set returns PREF_VALUECHANGED if the user value changed
+// (triggering a callback), or PREF_NOERROR if the value was unchanged.
+// </font>
+*/
+nsresult PREF_SetCharPref(const char *pref,const char* value, bool set_default = false);
+nsresult PREF_SetIntPref(const char *pref,int32_t value, bool set_default = false);
+nsresult PREF_SetBoolPref(const char *pref,bool value, bool set_default = false);
+
+bool     PREF_HasUserPref(const char* pref_name);
+
+/*
+// <font color=blue>
+// Get the various types of preferences.  These functions take a dotted
+// notation of the preference name (e.g. "browser.startup.homepage")
+//
+// They also take a pointer to fill in with the return value and return an
+// error value.  At the moment, this is simply an int but it may
+// be converted to an enum once the global error strategy is worked out.
+//
+// They will perform conversion if the type doesn't match what was requested.
+// (if it is reasonably possible)
+// </font>
+*/
+nsresult PREF_GetIntPref(const char *pref,
+                           int32_t * return_int, bool get_default);
+nsresult PREF_GetBoolPref(const char *pref, bool * return_val, bool get_default);
+/*
+// <font color=blue>
+// These functions are similar to the above "Get" version with the significant
+// difference that the preference module will alloc the memory (e.g. XP_STRDUP) and
+// the caller will need to be responsible for freeing it...
+// </font>
+*/
+nsresult PREF_CopyCharPref(const char *pref, char ** return_buf, bool get_default);
+/*
+// <font color=blue>
+// bool function that returns whether or not the preference is locked and therefore
+// cannot be changed.
+// </font>
+*/
+bool PREF_PrefIsLocked(const char *pref_name);
+
+/*
+// <font color=blue>
+// Function that sets whether or not the preference is locked and therefore
+// cannot be changed.
+// </font>
+*/
+nsresult PREF_LockPref(const char *key, bool lockIt);
+
+PrefType PREF_GetPrefType(const char *pref_name);
+
+/*
+ * Delete a branch of the tree
+ */
+nsresult PREF_DeleteBranch(const char *branch_name);
+
+/*
+ * Clears the given pref (reverts it to its default value)
+ */
+nsresult PREF_ClearUserPref(const char *pref_name);
+
+/*
+ * Clears all user prefs
+ */
+nsresult PREF_ClearAllUserPrefs();
+
+
+/*
+// <font color=blue>
+// The callback function will get passed the pref_node which triggered the call
+// and the void * instance_data which was passed to the register callback function.
+// Return a non-zero result (nsresult) to pass an error up to the caller.
+// </font>
+*/
+/* Temporarily conditionally compile PrefChangedFunc typedef.
+** During migration from old libpref to nsIPref we need it in
+** both header files.  Eventually prefapi.h will become a private
+** file.  The two types need to be in sync for now.  Certain
+** compilers were having problems with multiple definitions.
+*/
+#ifndef have_PrefChangedFunc_typedef
+typedef void (*PrefChangedFunc) (const char *, void *);
+#define have_PrefChangedFunc_typedef
+#endif
+
+/*
+// <font color=blue>
+// Register a callback.  This takes a node in the preference tree and will
+// call the callback function if anything below that node is modified.
+// Unregister returns PREF_NOERROR if a callback was found that
+// matched all the parameters; otherwise it returns PREF_ERROR.
+// </font>
+*/
+void PREF_RegisterCallback(const char* domain,
+                           PrefChangedFunc callback, void* instance_data );
+nsresult PREF_UnregisterCallback(const char* domain,
+                                 PrefChangedFunc callback, void* instance_data );
+
+/*
+ * Used by nsPrefService as the callback function of the 'pref' parser
+ */
+void PREF_ReaderCallback( void *closure,
+                          const char *pref,
+                          PrefValue   value,
+                          PrefType    type,
+                          bool        isDefault,
+                          bool        isStickyDefault);
+
+
+/*
+ * Callback whenever we change a preference
+ */
+typedef void (*PrefsDirtyFunc) ();
+void PREF_SetDirtyCallback(PrefsDirtyFunc);
+
+#ifdef __cplusplus
+}
+#endif
+#endif
diff --git a/components/preferences/src/prefapi_private_data.h b/components/preferences/src/prefapi_private_data.h
new file mode 100644
index 000000000..f1fa68fdc
--- /dev/null
+++ b/components/preferences/src/prefapi_private_data.h
@@ -0,0 +1,40 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Data shared between prefapi.c and nsPref.cpp */
+
+#ifndef prefapi_private_data_h
+#define prefapi_private_data_h
+
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/UniquePtr.h"
+
+extern PLDHashTable* gHashTable;
+
+namespace mozilla {
+namespace dom {
+class PrefSetting;
+} // namespace dom
+} // namespace mozilla
+
+mozilla::UniquePtr<char*[]>
+pref_savePrefs(PLDHashTable* aTable, uint32_t* aPrefCount);
+
+nsresult
+pref_SetPref(const mozilla::dom::PrefSetting& aPref);
+
+int pref_CompareStrings(const void *v1, const void *v2, void* unused);
+PrefHashEntry* pref_HashTableLookup(const char *key);
+
+bool
+pref_EntryHasAdvisablySizedValues(PrefHashEntry* aHashEntry);
+
+void pref_GetPrefFromEntry(PrefHashEntry *aHashEntry,
+                           mozilla::dom::PrefSetting* aPref);
+
+size_t
+pref_SizeOfPrivateData(mozilla::MallocSizeOf aMallocSizeOf);
+
+#endif
diff --git a/components/preferences/src/prefread.cpp b/components/preferences/src/prefread.cpp
new file mode 100644
index 000000000..605dcaac6
--- /dev/null
+++ b/components/preferences/src/prefread.cpp
@@ -0,0 +1,657 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include "prefread.h"
+#include "nsString.h"
+#include "nsUTF8Utils.h"
+
+#ifdef TEST_PREFREAD
+#include <stdio.h>
+#define NS_WARNING(_s) printf(">>> " _s "!\n")
+#define NS_NOTREACHED(_s) NS_WARNING(_s)
+#else
+#include "nsDebug.h" // for NS_WARNING
+#endif
+
+/* pref parser states */
+enum {
+    PREF_PARSE_INIT,
+    PREF_PARSE_MATCH_STRING,
+    PREF_PARSE_UNTIL_NAME,
+    PREF_PARSE_QUOTED_STRING,
+    PREF_PARSE_UNTIL_COMMA,
+    PREF_PARSE_UNTIL_VALUE,
+    PREF_PARSE_INT_VALUE,
+    PREF_PARSE_COMMENT_MAYBE_START,
+    PREF_PARSE_COMMENT_BLOCK,
+    PREF_PARSE_COMMENT_BLOCK_MAYBE_END,
+    PREF_PARSE_ESC_SEQUENCE,
+    PREF_PARSE_HEX_ESCAPE,
+    PREF_PARSE_UTF16_LOW_SURROGATE,
+    PREF_PARSE_UNTIL_OPEN_PAREN,
+    PREF_PARSE_UNTIL_CLOSE_PAREN,
+    PREF_PARSE_UNTIL_SEMICOLON,
+    PREF_PARSE_UNTIL_EOL
+};
+
+#define UTF16_ESC_NUM_DIGITS    4
+#define HEX_ESC_NUM_DIGITS      2
+#define BITS_PER_HEX_DIGIT      4
+
+static const char kUserPref[] = "user_pref";
+static const char kPref[] = "pref";
+static const char kPrefSticky[] = "sticky_pref";
+static const char kTrue[] = "true";
+static const char kFalse[] = "false";
+
+/**
+ * pref_GrowBuf
+ * 
+ * this function will increase the size of the buffer owned
+ * by the given pref parse state.  We currently use a simple
+ * doubling algorithm, but the only hard requirement is that
+ * it increase the buffer by at least the size of the ps->esctmp
+ * buffer used for escape processing (currently 6 bytes).
+ * 
+ * this buffer is used to store partial pref lines.  it is
+ * freed when the parse state is destroyed.
+ *
+ * @param ps
+ *        parse state instance
+ *
+ * this function updates all pointers that reference an 
+ * address within lb since realloc may relocate the buffer.
+ *
+ * @return false if insufficient memory.
+ */
+static bool
+pref_GrowBuf(PrefParseState *ps)
+{
+    int bufLen, curPos, valPos;
+
+    bufLen = ps->lbend - ps->lb;
+    curPos = ps->lbcur - ps->lb;
+    valPos = ps->vb    - ps->lb;
+
+    if (bufLen == 0)
+        bufLen = 128;  /* default buffer size */
+    else
+        bufLen <<= 1;  /* double buffer size */
+
+#ifdef TEST_PREFREAD
+    fprintf(stderr, ">>> realloc(%d)\n", bufLen);
+#endif
+
+    ps->lb = (char*) realloc(ps->lb, bufLen);
+    if (!ps->lb)
+        return false;
+
+    ps->lbcur = ps->lb + curPos;
+    ps->lbend = ps->lb + bufLen;
+    ps->vb    = ps->lb + valPos;
+
+    return true;
+}
+
+/**
+ * Report an error or a warning.  If not specified, just dump to stderr.
+ */
+static void
+pref_ReportParseProblem(PrefParseState& ps, const char* aMessage, int aLine, bool aError)
+{
+    if (ps.reporter) {
+        ps.reporter(aMessage, aLine, aError);
+    } else {
+        printf_stderr("**** Preference parsing %s (line %d) = %s **\n",
+                      (aError ? "error" : "warning"), aLine, aMessage);
+    }
+}
+
+/**
+ * pref_DoCallback
+ *
+ * this function is called when a complete pref name-value pair has
+ * been extracted from the input data.
+ *
+ * @param ps
+ *        parse state instance
+ *
+ * @return false to indicate a fatal error.
+ */
+static bool
+pref_DoCallback(PrefParseState *ps)
+{
+    PrefValue  value;
+
+    switch (ps->vtype) {
+    case PrefType::String:
+        value.stringVal = ps->vb;
+        break;
+    case PrefType::Int:
+        if ((ps->vb[0] == '-' || ps->vb[0] == '+') && ps->vb[1] == '\0') {
+            pref_ReportParseProblem(*ps, "invalid integer value", 0, true);
+            NS_WARNING("malformed integer value");
+            return false;
+        }
+        value.intVal = atoi(ps->vb);
+        break;
+    case PrefType::Bool:
+        value.boolVal = (ps->vb == kTrue);
+        break;
+    default:
+        break;
+    }
+    (*ps->reader)(ps->closure, ps->lb, value, ps->vtype, ps->fdefault,
+                  ps->fstickydefault);
+    return true;
+}
+
+void
+PREF_InitParseState(PrefParseState *ps, PrefReader reader,
+                    PrefParseErrorReporter reporter, void *closure)
+{
+    memset(ps, 0, sizeof(*ps));
+    ps->reader = reader;
+    ps->closure = closure;
+    ps->reporter = reporter;
+}
+
+void
+PREF_FinalizeParseState(PrefParseState *ps)
+{
+    if (ps->lb)
+        free(ps->lb);
+}
+
+/**
+ * Pseudo-BNF
+ * ----------
+ * function      = LJUNK function-name JUNK function-args
+ * function-name = "user_pref" | "pref" | "sticky_pref"
+ * function-args = "(" JUNK pref-name JUNK "," JUNK pref-value JUNK ")" JUNK ";"
+ * pref-name     = quoted-string
+ * pref-value    = quoted-string | "true" | "false" | integer-value
+ * JUNK          = *(WS | comment-block | comment-line)
+ * LJUNK         = *(WS | comment-block | comment-line | bcomment-line)
+ * WS            = SP | HT | LF | VT | FF | CR
+ * SP            = <US-ASCII SP, space (32)>
+ * HT            = <US-ASCII HT, horizontal-tab (9)>
+ * LF            = <US-ASCII LF, linefeed (10)>
+ * VT            = <US-ASCII HT, vertical-tab (11)>
+ * FF            = <US-ASCII FF, form-feed (12)>
+ * CR            = <US-ASCII CR, carriage return (13)>
+ * comment-block = <C/C++ style comment block>
+ * comment-line  = <C++ style comment line>
+ * bcomment-line = <bourne-shell style comment line>
+ */
+bool
+PREF_ParseBuf(PrefParseState *ps, const char *buf, int bufLen)
+{
+    const char *end;
+    char c;
+    char udigit;
+    int state;
+
+    // The line number is currently only used for the error/warning reporting.
+    int lineNum = 0;
+
+    state = ps->state;
+    for (end = buf + bufLen; buf != end; ++buf) {
+        c = *buf;
+        if (c == '\r' || c == '\n' || c == 0x1A) {
+            lineNum ++;
+        }
+
+        switch (state) {
+        /* initial state */
+        case PREF_PARSE_INIT:
+            if (ps->lbcur != ps->lb) { /* reset state */
+                ps->lbcur = ps->lb;
+                ps->vb    = nullptr;
+                ps->vtype = PrefType::Invalid;
+                ps->fdefault = false;
+                ps->fstickydefault = false;
+            }
+            switch (c) {
+            case '/':       /* begin comment block or line? */
+                state = PREF_PARSE_COMMENT_MAYBE_START;
+                break;
+            case '#':       /* accept shell style comments */
+                state = PREF_PARSE_UNTIL_EOL;
+                break;
+            case 'u':       /* indicating user_pref */
+            case 's':       /* indicating sticky_pref */
+            case 'p':       /* indicating pref */
+                if (c == 'u') {
+                  ps->smatch = kUserPref;
+                } else if (c == 's') {
+                  ps->smatch = kPrefSticky;
+                } else {
+                  ps->smatch = kPref;
+                }
+                ps->sindex = 1;
+                ps->nextstate = PREF_PARSE_UNTIL_OPEN_PAREN;
+                state = PREF_PARSE_MATCH_STRING;
+                break;
+            /* else skip char */
+            }
+            break;
+
+        /* string matching */
+        case PREF_PARSE_MATCH_STRING:
+            if (c == ps->smatch[ps->sindex++]) {
+                /* if we've matched all characters, then move to next state. */
+                if (ps->smatch[ps->sindex] == '\0') {
+                    state = ps->nextstate;
+                    ps->nextstate = PREF_PARSE_INIT; /* reset next state */
+                }
+                /* else wait for next char */
+            }
+            else {
+                pref_ReportParseProblem(*ps, "non-matching string", lineNum, true);
+                NS_WARNING("malformed pref file");
+                return false;
+            }
+            break;
+
+        /* quoted string parsing */
+        case PREF_PARSE_QUOTED_STRING:
+            /* we assume that the initial quote has already been consumed */
+            if (ps->lbcur == ps->lbend && !pref_GrowBuf(ps))
+                return false; /* out of memory */
+            if (c == '\\')
+                state = PREF_PARSE_ESC_SEQUENCE;
+            else if (c == ps->quotechar) {
+                *ps->lbcur++ = '\0';
+                state = ps->nextstate;
+                ps->nextstate = PREF_PARSE_INIT; /* reset next state */
+            }
+            else
+                *ps->lbcur++ = c;
+            break;
+
+        /* name parsing */
+        case PREF_PARSE_UNTIL_NAME:
+            if (c == '\"' || c == '\'') {
+                ps->fdefault = (ps->smatch == kPref || ps->smatch == kPrefSticky);
+                ps->fstickydefault = (ps->smatch == kPrefSticky);
+                ps->quotechar = c;
+                ps->nextstate = PREF_PARSE_UNTIL_COMMA; /* return here when done */
+                state = PREF_PARSE_QUOTED_STRING;
+            }
+            else if (c == '/') {       /* allow embedded comment */
+                ps->nextstate = state; /* return here when done with comment */
+                state = PREF_PARSE_COMMENT_MAYBE_START;
+            }
+            else if (!isspace(c)) {
+                pref_ReportParseProblem(*ps, "need space, comment or quote", lineNum, true);
+                NS_WARNING("malformed pref file");
+                return false;
+            }
+            break;
+
+        /* parse until we find a comma separating name and value */
+        case PREF_PARSE_UNTIL_COMMA:
+            if (c == ',') {
+                ps->vb = ps->lbcur;
+                state = PREF_PARSE_UNTIL_VALUE;
+            }
+            else if (c == '/') {       /* allow embedded comment */
+                ps->nextstate = state; /* return here when done with comment */
+                state = PREF_PARSE_COMMENT_MAYBE_START;
+            }
+            else if (!isspace(c)) {
+                pref_ReportParseProblem(*ps, "need space, comment or comma", lineNum, true);
+                NS_WARNING("malformed pref file");
+                return false;
+            }
+            break;
+
+        /* value parsing */
+        case PREF_PARSE_UNTIL_VALUE:
+            /* the pref value type is unknown.  so, we scan for the first
+             * character of the value, and determine the type from that. */
+            if (c == '\"' || c == '\'') {
+                ps->vtype = PrefType::String;
+                ps->quotechar = c;
+                ps->nextstate = PREF_PARSE_UNTIL_CLOSE_PAREN;
+                state = PREF_PARSE_QUOTED_STRING;
+            }
+            else if (c == 't' || c == 'f') {
+                ps->vb = (char *) (c == 't' ? kTrue : kFalse);
+                ps->vtype = PrefType::Bool;
+                ps->smatch = ps->vb;
+                ps->sindex = 1;
+                ps->nextstate = PREF_PARSE_UNTIL_CLOSE_PAREN;
+                state = PREF_PARSE_MATCH_STRING;
+            }
+            else if (isdigit(c) || (c == '-') || (c == '+')) {
+                ps->vtype = PrefType::Int;
+                /* write c to line buffer... */
+                if (ps->lbcur == ps->lbend && !pref_GrowBuf(ps))
+                    return false; /* out of memory */
+                *ps->lbcur++ = c;
+                state = PREF_PARSE_INT_VALUE;
+            }
+            else if (c == '/') {       /* allow embedded comment */
+                ps->nextstate = state; /* return here when done with comment */
+                state = PREF_PARSE_COMMENT_MAYBE_START;
+            }
+            else if (!isspace(c)) {
+                pref_ReportParseProblem(*ps, "need value, comment or space", lineNum, true);
+                NS_WARNING("malformed pref file");
+                return false;
+            }
+            break;
+        case PREF_PARSE_INT_VALUE:
+            /* grow line buffer if necessary... */
+            if (ps->lbcur == ps->lbend && !pref_GrowBuf(ps))
+                return false; /* out of memory */
+            if (isdigit(c))
+                *ps->lbcur++ = c;
+            else {
+                *ps->lbcur++ = '\0'; /* stomp null terminator; we are done. */
+                if (c == ')')
+                    state = PREF_PARSE_UNTIL_SEMICOLON;
+                else if (c == '/') { /* allow embedded comment */
+                    ps->nextstate = PREF_PARSE_UNTIL_CLOSE_PAREN;
+                    state = PREF_PARSE_COMMENT_MAYBE_START;
+                }
+                else if (isspace(c))
+                    state = PREF_PARSE_UNTIL_CLOSE_PAREN;
+                else {
+                    pref_ReportParseProblem(*ps, "while parsing integer", lineNum, true);
+                    NS_WARNING("malformed pref file");
+                    return false;
+                }
+            }
+            break;
+
+        /* comment parsing */
+        case PREF_PARSE_COMMENT_MAYBE_START:
+            switch (c) {
+            case '*': /* comment block */
+                state = PREF_PARSE_COMMENT_BLOCK;
+                break;
+            case '/': /* comment line */
+                state = PREF_PARSE_UNTIL_EOL;
+                break;
+            default:
+                /* pref file is malformed */
+                pref_ReportParseProblem(*ps, "while parsing comment", lineNum, true);
+                NS_WARNING("malformed pref file");
+                return false;
+            }
+            break;
+        case PREF_PARSE_COMMENT_BLOCK:
+            if (c == '*')
+                state = PREF_PARSE_COMMENT_BLOCK_MAYBE_END;
+            break;
+        case PREF_PARSE_COMMENT_BLOCK_MAYBE_END:
+            switch (c) {
+            case '/':
+                state = ps->nextstate;
+                ps->nextstate = PREF_PARSE_INIT;
+                break;
+            case '*':       /* stay in this state */
+                break;
+            default:
+                state = PREF_PARSE_COMMENT_BLOCK;
+            }
+            break;
+
+        /* string escape sequence parsing */
+        case PREF_PARSE_ESC_SEQUENCE:
+            /* not necessary to resize buffer here since we should be writing
+             * only one character and the resize check would have been done
+             * for us in the previous state */
+            switch (c) {
+            case '\"':
+            case '\'':
+            case '\\':
+                break;
+            case 'r':
+                c = '\r';
+                break;
+            case 'n':
+                c = '\n';
+                break;
+            case 'x': /* hex escape -- always interpreted as Latin-1 */
+            case 'u': /* UTF16 escape */
+                ps->esctmp[0] = c;
+                ps->esclen = 1;
+                ps->utf16[0] = ps->utf16[1] = 0;
+                ps->sindex = (c == 'x' ) ?
+                                HEX_ESC_NUM_DIGITS :
+                                UTF16_ESC_NUM_DIGITS;
+                state = PREF_PARSE_HEX_ESCAPE;
+                continue;
+            default:
+                pref_ReportParseProblem(*ps, "preserving unexpected JS escape sequence",
+                                        lineNum, false);
+                NS_WARNING("preserving unexpected JS escape sequence");
+                /* Invalid escape sequence so we do have to write more than
+                 * one character. Grow line buffer if necessary... */
+                if ((ps->lbcur+1) == ps->lbend && !pref_GrowBuf(ps))
+                    return false; /* out of memory */
+                *ps->lbcur++ = '\\'; /* preserve the escape sequence */
+                break;
+            }
+            *ps->lbcur++ = c;
+            state = PREF_PARSE_QUOTED_STRING;
+            break;
+
+        /* parsing a hex (\xHH) or utf16 escape (\uHHHH) */
+        case PREF_PARSE_HEX_ESCAPE:
+            if ( c >= '0' && c <= '9' )
+                udigit = (c - '0');
+            else if ( c >= 'A' && c <= 'F' )
+                udigit = (c - 'A') + 10;
+            else if ( c >= 'a' && c <= 'f' )
+                udigit = (c - 'a') + 10;
+            else {
+                /* bad escape sequence found, write out broken escape as-is */
+                pref_ReportParseProblem(*ps, "preserving invalid or incomplete hex escape",
+                                        lineNum, false);
+                NS_WARNING("preserving invalid or incomplete hex escape");
+                *ps->lbcur++ = '\\';  /* original escape slash */
+                if ((ps->lbcur + ps->esclen) >= ps->lbend && !pref_GrowBuf(ps))
+                    return false;
+                for (int i = 0; i < ps->esclen; ++i)
+                    *ps->lbcur++ = ps->esctmp[i];
+
+                /* push the non-hex character back for re-parsing. */
+                /* (++buf at the top of the loop keeps this safe)  */
+                --buf;
+                state = PREF_PARSE_QUOTED_STRING;
+                continue;
+            }
+
+            /* have a digit */
+            ps->esctmp[ps->esclen++] = c; /* preserve it */
+            ps->utf16[1] <<= BITS_PER_HEX_DIGIT;
+            ps->utf16[1] |= udigit;
+            ps->sindex--;
+            if (ps->sindex == 0) {
+                /* have the full escape. Convert to UTF8 */
+                int utf16len = 0;
+                if (ps->utf16[0]) {
+                    /* already have a high surrogate, this is a two char seq */
+                    utf16len = 2;
+                }
+                else if (0xD800 == (0xFC00 & ps->utf16[1])) {
+                    /* a high surrogate, can't convert until we have the low */
+                    ps->utf16[0] = ps->utf16[1];
+                    ps->utf16[1] = 0;
+                    state = PREF_PARSE_UTF16_LOW_SURROGATE;
+                    break;
+                }
+                else {
+                    /* a single utf16 character */
+                    ps->utf16[0] = ps->utf16[1];
+                    utf16len = 1;
+                }
+
+                /* actual conversion */
+                /* make sure there's room, 6 bytes is max utf8 len (in */
+                /* theory; 4 bytes covers the actual utf16 range) */
+                if (ps->lbcur+6 >= ps->lbend && !pref_GrowBuf(ps))
+                    return false;
+
+                ConvertUTF16toUTF8 converter(ps->lbcur);
+                converter.write(ps->utf16, utf16len);
+                ps->lbcur += converter.Size();
+                state = PREF_PARSE_QUOTED_STRING;
+            }
+            break;
+
+        /* looking for beginning of utf16 low surrogate */
+        case PREF_PARSE_UTF16_LOW_SURROGATE:
+            if (ps->sindex == 0 && c == '\\') {
+                ++ps->sindex;
+            }
+            else if (ps->sindex == 1 && c == 'u') {
+                /* escape sequence is correct, now parse hex */
+                ps->sindex = UTF16_ESC_NUM_DIGITS;
+                ps->esctmp[0] = 'u';
+                ps->esclen = 1;
+                state = PREF_PARSE_HEX_ESCAPE;
+            }
+            else {
+                /* didn't find expected low surrogate. Ignore high surrogate
+                 * (it would just get converted to nothing anyway) and start
+                 * over with this character */
+                 --buf;
+                 if (ps->sindex == 1)
+                     state = PREF_PARSE_ESC_SEQUENCE;
+                 else
+                     state = PREF_PARSE_QUOTED_STRING;
+                 continue;
+            }
+            break;
+
+        /* function open and close parsing */
+        case PREF_PARSE_UNTIL_OPEN_PAREN:
+            /* tolerate only whitespace and embedded comments */
+            if (c == '(')
+                state = PREF_PARSE_UNTIL_NAME;
+            else if (c == '/') {
+                ps->nextstate = state; /* return here when done with comment */
+                state = PREF_PARSE_COMMENT_MAYBE_START;
+            }
+            else if (!isspace(c)) {
+                pref_ReportParseProblem(*ps, "need space, comment or open parentheses",
+                                        lineNum, true);
+                NS_WARNING("malformed pref file");
+                return false;
+            }
+            break;
+        case PREF_PARSE_UNTIL_CLOSE_PAREN:
+            /* tolerate only whitespace and embedded comments  */
+            if (c == ')') {
+                state = PREF_PARSE_UNTIL_SEMICOLON;
+            } else if (c == '/') {
+                ps->nextstate = state; /* return here when done with comment */
+                state = PREF_PARSE_COMMENT_MAYBE_START;
+            } else if (!isspace(c)) {
+                pref_ReportParseProblem(*ps, "need space, comment or closing parentheses",
+                                        lineNum, true);
+                NS_WARNING("malformed pref file");
+                return false;
+            }
+            break;
+
+        /* function terminator ';' parsing */
+        case PREF_PARSE_UNTIL_SEMICOLON:
+            /* tolerate only whitespace and embedded comments */
+            if (c == ';') {
+                if (!pref_DoCallback(ps))
+                    return false;
+                state = PREF_PARSE_INIT;
+            }
+            else if (c == '/') {
+                ps->nextstate = state; /* return here when done with comment */
+                state = PREF_PARSE_COMMENT_MAYBE_START;
+            }
+            else if (!isspace(c)) {
+                pref_ReportParseProblem(*ps, "need space, comment or semicolon",
+                                        lineNum, true);
+                NS_WARNING("malformed pref file");
+                return false;
+            }
+            break;
+
+        /* eol parsing */
+        case PREF_PARSE_UNTIL_EOL:
+            /* need to handle mac, unix, or dos line endings.
+             * PREF_PARSE_INIT will eat the next \n in case
+             * we have \r\n. */
+            if (c == '\r' || c == '\n' || c == 0x1A) {
+                state = ps->nextstate;
+                ps->nextstate = PREF_PARSE_INIT; /* reset next state */
+            }
+            break;
+        }
+    }
+    ps->state = state;
+    return true;
+}
+
+#ifdef TEST_PREFREAD
+
+static void
+pref_reader(void       *closure, 
+            const char *pref,
+            PrefValue   val,
+            PrefType    type,
+            bool        defPref)
+{
+    printf("%spref(\"%s\", ", defPref ? "" : "user_", pref);
+    switch (type) {
+    case PREF_STRING:
+        printf("\"%s\");\n", val.stringVal);
+        break;
+    case PREF_INT:
+        printf("%i);\n", val.intVal);
+        break;
+    case PREF_BOOL:
+        printf("%s);\n", val.boolVal == false ? "false" : "true");
+        break;
+    }
+}
+
+int
+main(int argc, char **argv)
+{
+    PrefParseState ps;
+    char buf[4096];     /* i/o buffer */
+    FILE *fp;
+    int n;
+
+    if (argc == 1) {
+        printf("usage: prefread file.js\n");
+        return -1;
+    }
+
+    fp = fopen(argv[1], "r");
+    if (!fp) {
+        printf("failed to open file\n");
+        return -1;
+    }
+
+    PREF_InitParseState(&ps, pref_reader, nullptr, nullptr);
+
+    while ((n = fread(buf, 1, sizeof(buf), fp)) > 0)
+        PREF_ParseBuf(&ps, buf, n);
+
+    PREF_FinalizeParseState(&ps);
+
+    fclose(fp);
+    return 0;
+}
+
+#endif /* TEST_PREFREAD */
diff --git a/components/preferences/src/prefread.h b/components/preferences/src/prefread.h
new file mode 100644
index 000000000..2a09b30b6
--- /dev/null
+++ b/components/preferences/src/prefread.h
@@ -0,0 +1,118 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef prefread_h__
+#define prefread_h__
+
+#include "prefapi.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Callback function used to notify consumer of preference name value pairs.
+ * The pref name and value must be copied by the implementor of the callback
+ * if they are needed beyond the scope of the callback function.
+ *
+ * @param closure
+ *        user data passed to PREF_InitParseState
+ * @param pref
+ *        preference name
+ * @param val
+ *        preference value
+ * @param type
+ *        preference type (PREF_STRING, PREF_INT, or PREF_BOOL)
+ * @param defPref
+ *        preference type (true: default, false: user preference)
+ * @param stickyPref
+ *        default preference marked as a "sticky" pref
+ */
+typedef void (*PrefReader)(void       *closure,
+                           const char *pref,
+                           PrefValue   val,
+                           PrefType    type,
+                           bool        defPref,
+                           bool        stickyPref);
+
+/**
+ * Report any errors or warnings we encounter during parsing.
+ */
+typedef void (*PrefParseErrorReporter)(const char* message, int line, bool error);
+
+/* structure fields are private */
+typedef struct PrefParseState {
+    PrefReader  reader;
+    PrefParseErrorReporter reporter;
+    void       *closure;
+    int         state;      /* PREF_PARSE_...                */
+    int         nextstate;  /* sometimes used...             */
+    const char *smatch;     /* string to match               */
+    int         sindex;     /* next char of smatch to check  */
+                            /* also, counter in \u parsing   */
+    char16_t   utf16[2];   /* parsing UTF16  (\u) escape    */
+    int         esclen;     /* length in esctmp              */
+    char        esctmp[6];  /* raw escape to put back if err */
+    char        quotechar;  /* char delimiter for quotations */
+    char       *lb;         /* line buffer (only allocation) */
+    char       *lbcur;      /* line buffer cursor            */
+    char       *lbend;      /* line buffer end               */
+    char       *vb;         /* value buffer (ptr into lb)    */
+    PrefType    vtype;      /* PREF_STRING,INT,BOOL          */
+    bool        fdefault;   /* true if (default) pref        */
+    bool        fstickydefault; /* true if (sticky) pref     */
+} PrefParseState;
+
+/**
+ * PREF_InitParseState
+ *
+ * Called to initialize a PrefParseState instance.
+ *
+ * @param ps
+ *        PrefParseState instance.
+ * @param reader
+ *        PrefReader callback function, which will be called once for each
+ *        preference name value pair extracted.
+ * @param reporter
+ *        PrefParseErrorReporter callback function, which will be called if we
+ *        encounter any errors (stop) or warnings (continue) during parsing.
+ * @param closure
+ *        PrefReader closure.
+ */
+void PREF_InitParseState(PrefParseState *ps, PrefReader reader,
+			 PrefParseErrorReporter reporter, void *closure);
+
+/**
+ * PREF_FinalizeParseState
+ *
+ * Called to release any memory in use by the PrefParseState instance.
+ *
+ * @param ps
+ *        PrefParseState instance.
+ */        
+void PREF_FinalizeParseState(PrefParseState *ps);
+
+/**
+ * PREF_ParseBuf
+ *
+ * Called to parse a buffer containing some portion of a preference file.  This
+ * function may be called repeatedly as new data is made available.  The
+ * PrefReader callback function passed PREF_InitParseState will be called as
+ * preference name value pairs are extracted from the data.
+ *
+ * @param ps
+ *        PrefParseState instance.  Must have been initialized.
+ * @param buf
+ *        Raw buffer containing data to be parsed.
+ * @param bufLen
+ *        Length of buffer.
+ *
+ * @return false if buffer contains malformed content.
+ */
+bool PREF_ParseBuf(PrefParseState *ps, const char *buf, int bufLen);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* prefread_h__ */