Add m-esr52 at 52.6.0

16 files changed, 6205 insertions, 0 deletions

diff --git a/dom/storage/DOMStorage.cpp b/dom/storage/DOMStorage.cpp
new file mode 100644
index 0000000000..026959dcec
--- /dev/null
+++ b/dom/storage/DOMStorage.cpp
@@ -0,0 +1,301 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "DOMStorage.h"
+#include "DOMStorageCache.h"
+#include "DOMStorageManager.h"
+
+#include "nsIObserverService.h"
+#include "nsIScriptSecurityManager.h"
+#include "nsIPermissionManager.h"
+#include "nsIPrincipal.h"
+#include "nsICookiePermission.h"
+#include "nsPIDOMWindow.h"
+
+#include "mozilla/dom/StorageBinding.h"
+#include "mozilla/dom/StorageEvent.h"
+#include "mozilla/dom/StorageEventBinding.h"
+#include "mozilla/Services.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/EnumSet.h"
+#include "nsThreadUtils.h"
+#include "nsContentUtils.h"
+#include "nsServiceManagerUtils.h"
+
+namespace mozilla {
+namespace dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(DOMStorage, mManager, mPrincipal, mWindow)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(DOMStorage)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(DOMStorage)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(DOMStorage)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIDOMStorage)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMStorage)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+NS_INTERFACE_MAP_END
+
+DOMStorage::DOMStorage(nsPIDOMWindowInner* aWindow,
+                       DOMStorageManager* aManager,
+                       DOMStorageCache* aCache,
+                       const nsAString& aDocumentURI,
+                       nsIPrincipal* aPrincipal,
+                       bool aIsPrivate)
+: mWindow(aWindow)
+, mManager(aManager)
+, mCache(aCache)
+, mDocumentURI(aDocumentURI)
+, mPrincipal(aPrincipal)
+, mIsPrivate(aIsPrivate)
+, mIsSessionOnly(false)
+{
+  mCache->Preload();
+}
+
+DOMStorage::~DOMStorage()
+{
+  mCache->KeepAlive();
+}
+
+/* virtual */ JSObject*
+DOMStorage::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
+{
+  return StorageBinding::Wrap(aCx, this, aGivenProto);
+}
+
+uint32_t
+DOMStorage::GetLength(nsIPrincipal& aSubjectPrincipal,
+                      ErrorResult& aRv)
+{
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return 0;
+  }
+
+  uint32_t length;
+  aRv = mCache->GetLength(this, &length);
+  return length;
+}
+
+void
+DOMStorage::Key(uint32_t aIndex, nsAString& aResult,
+                nsIPrincipal& aSubjectPrincipal,
+                ErrorResult& aRv)
+{
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  aRv = mCache->GetKey(this, aIndex, aResult);
+}
+
+void
+DOMStorage::GetItem(const nsAString& aKey, nsAString& aResult,
+                    nsIPrincipal& aSubjectPrincipal,
+                    ErrorResult& aRv)
+{
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  aRv = mCache->GetItem(this, aKey, aResult);
+}
+
+void
+DOMStorage::SetItem(const nsAString& aKey, const nsAString& aData,
+                    nsIPrincipal& aSubjectPrincipal,
+                    ErrorResult& aRv)
+{
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsString data;
+  bool ok = data.Assign(aData, fallible);
+  if (!ok) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+
+  nsString old;
+  aRv = mCache->SetItem(this, aKey, data, old);
+  if (aRv.Failed()) {
+    return;
+  }
+
+  if (!aRv.ErrorCodeIs(NS_SUCCESS_DOM_NO_OPERATION)) {
+    BroadcastChangeNotification(aKey, old, aData);
+  }
+}
+
+void
+DOMStorage::RemoveItem(const nsAString& aKey,
+                       nsIPrincipal& aSubjectPrincipal,
+                       ErrorResult& aRv)
+{
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsAutoString old;
+  aRv = mCache->RemoveItem(this, aKey, old);
+  if (aRv.Failed()) {
+    return;
+  }
+
+  if (!aRv.ErrorCodeIs(NS_SUCCESS_DOM_NO_OPERATION)) {
+    BroadcastChangeNotification(aKey, old, NullString());
+  }
+}
+
+void
+DOMStorage::Clear(nsIPrincipal& aSubjectPrincipal,
+                  ErrorResult& aRv)
+{
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  aRv = mCache->Clear(this);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  if (!aRv.ErrorCodeIs(NS_SUCCESS_DOM_NO_OPERATION)) {
+    BroadcastChangeNotification(NullString(), NullString(), NullString());
+  }
+}
+
+namespace {
+
+class StorageNotifierRunnable : public Runnable
+{
+public:
+  StorageNotifierRunnable(nsISupports* aSubject, const char16_t* aType)
+    : mSubject(aSubject), mType(aType)
+  { }
+
+  NS_DECL_NSIRUNNABLE
+
+private:
+  nsCOMPtr<nsISupports> mSubject;
+  const char16_t* mType;
+};
+
+NS_IMETHODIMP
+StorageNotifierRunnable::Run()
+{
+  nsCOMPtr<nsIObserverService> observerService =
+    mozilla::services::GetObserverService();
+  if (observerService) {
+    observerService->NotifyObservers(mSubject, "dom-storage2-changed", mType);
+  }
+  return NS_OK;
+}
+
+} // namespace
+
+void
+DOMStorage::BroadcastChangeNotification(const nsSubstring& aKey,
+                                        const nsSubstring& aOldValue,
+                                        const nsSubstring& aNewValue)
+{
+  StorageEventInit dict;
+  dict.mBubbles = false;
+  dict.mCancelable = false;
+  dict.mKey = aKey;
+  dict.mNewValue = aNewValue;
+  dict.mOldValue = aOldValue;
+  dict.mStorageArea = this;
+  dict.mUrl = mDocumentURI;
+
+  // Note, this DOM event should never reach JS. It is cloned later in
+  // nsGlobalWindow.
+  RefPtr<StorageEvent> event =
+    StorageEvent::Constructor(nullptr, NS_LITERAL_STRING("storage"), dict);
+
+  RefPtr<StorageNotifierRunnable> r =
+    new StorageNotifierRunnable(event,
+                                GetType() == LocalStorage
+                                  ? u"localStorage"
+                                  : u"sessionStorage");
+  NS_DispatchToMainThread(r);
+}
+
+static const char kPermissionType[] = "cookie";
+static const char kStorageEnabled[] = "dom.storage.enabled";
+
+bool
+DOMStorage::CanUseStorage(nsIPrincipal& aSubjectPrincipal)
+{
+  // This method is responsible for correct setting of mIsSessionOnly.
+  // It doesn't work with mIsPrivate flag at all, since it is checked
+  // regardless mIsSessionOnly flag in DOMStorageCache code.
+
+  if (!mozilla::Preferences::GetBool(kStorageEnabled)) {
+    return false;
+  }
+
+  nsContentUtils::StorageAccess access =
+    nsContentUtils::StorageAllowedForPrincipal(mPrincipal);
+
+  if (access == nsContentUtils::StorageAccess::eDeny) {
+    return false;
+  }
+
+  mIsSessionOnly = access <= nsContentUtils::StorageAccess::eSessionScoped;
+  return CanAccess(&aSubjectPrincipal);
+}
+
+DOMStorage::StorageType
+DOMStorage::GetType() const
+{
+  return mManager->Type();
+}
+
+nsIPrincipal*
+DOMStorage::GetPrincipal()
+{
+  return mPrincipal;
+}
+
+// Defined in DOMStorageManager.cpp
+extern bool
+PrincipalsEqual(nsIPrincipal* aObjectPrincipal, nsIPrincipal* aSubjectPrincipal);
+
+bool
+DOMStorage::PrincipalEquals(nsIPrincipal* aPrincipal)
+{
+  return PrincipalsEqual(mPrincipal, aPrincipal);
+}
+
+bool
+DOMStorage::CanAccess(nsIPrincipal* aPrincipal)
+{
+  return !aPrincipal || aPrincipal->Subsumes(mPrincipal);
+}
+
+void
+DOMStorage::GetSupportedNames(nsTArray<nsString>& aKeys)
+{
+  if (!CanUseStorage(*nsContentUtils::SubjectPrincipal())) {
+    // return just an empty array
+    aKeys.Clear();
+    return;
+  }
+
+  mCache->GetKeys(this, aKeys);
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/DOMStorage.h b/dom/storage/DOMStorage.h
new file mode 100644
index 0000000000..d956ac3ed4
--- /dev/null
+++ b/dom/storage/DOMStorage.h
@@ -0,0 +1,172 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 nsDOMStorage_h___
+#define nsDOMStorage_h___
+
+#include "mozilla/Attributes.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/Maybe.h"
+#include "nsIDOMStorage.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsWeakReference.h"
+#include "nsWrapperCache.h"
+#include "nsISupports.h"
+
+class nsIPrincipal;
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+namespace dom {
+
+class DOMStorageManager;
+class DOMStorageCache;
+
+class DOMStorage final
+  : public nsIDOMStorage
+  , public nsSupportsWeakReference
+  , public nsWrapperCache
+{
+public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(DOMStorage,
+                                                         nsIDOMStorage)
+
+  enum StorageType {
+    LocalStorage = 1,
+    SessionStorage = 2
+  };
+
+  StorageType GetType() const;
+
+  DOMStorageManager* GetManager() const
+  {
+    return mManager;
+  }
+
+  DOMStorageCache const* GetCache() const
+  {
+    return mCache;
+  }
+
+  nsIPrincipal* GetPrincipal();
+  bool PrincipalEquals(nsIPrincipal* aPrincipal);
+  bool CanAccess(nsIPrincipal* aPrincipal);
+
+  DOMStorage(nsPIDOMWindowInner* aWindow,
+             DOMStorageManager* aManager,
+             DOMStorageCache* aCache,
+             const nsAString& aDocumentURI,
+             nsIPrincipal* aPrincipal,
+             bool aIsPrivate);
+
+  // WebIDL
+  JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
+
+  nsPIDOMWindowInner* GetParentObject() const
+  {
+    return mWindow;
+  }
+
+  uint32_t GetLength(nsIPrincipal& aSubjectPrincipal,
+                     ErrorResult& aRv);
+
+  void Key(uint32_t aIndex, nsAString& aResult,
+           nsIPrincipal& aSubjectPrincipal,
+           ErrorResult& aRv);
+
+  void GetItem(const nsAString& aKey, nsAString& aResult,
+               nsIPrincipal& aSubjectPrincipal,
+               ErrorResult& aRv);
+
+  void GetSupportedNames(nsTArray<nsString>& aKeys);
+
+  void NamedGetter(const nsAString& aKey, bool& aFound, nsAString& aResult,
+                   nsIPrincipal& aSubjectPrincipal,
+                   ErrorResult& aRv)
+  {
+    GetItem(aKey, aResult, aSubjectPrincipal, aRv);
+    aFound = !aResult.IsVoid();
+  }
+
+  void SetItem(const nsAString& aKey, const nsAString& aValue,
+               nsIPrincipal& aSubjectPrincipal,
+               ErrorResult& aRv);
+
+  void NamedSetter(const nsAString& aKey, const nsAString& aValue,
+                   nsIPrincipal& aSubjectPrincipal,
+                   ErrorResult& aRv)
+  {
+    SetItem(aKey, aValue, aSubjectPrincipal, aRv);
+  }
+
+  void RemoveItem(const nsAString& aKey,
+                  nsIPrincipal& aSubjectPrincipal,
+                  ErrorResult& aRv);
+
+  void NamedDeleter(const nsAString& aKey, bool& aFound,
+                    nsIPrincipal& aSubjectPrincipal,
+                    ErrorResult& aRv)
+  {
+    RemoveItem(aKey, aSubjectPrincipal, aRv);
+
+    aFound = !aRv.ErrorCodeIs(NS_SUCCESS_DOM_NO_OPERATION);
+  }
+
+  void Clear(nsIPrincipal& aSubjectPrincipal,
+             ErrorResult& aRv);
+
+  bool IsPrivate() const { return mIsPrivate; }
+  bool IsSessionOnly() const { return mIsSessionOnly; }
+
+  bool IsForkOf(const DOMStorage* aOther) const
+  {
+    MOZ_ASSERT(aOther);
+    return mCache == aOther->mCache;
+  }
+
+protected:
+  // The method checks whether the caller can use a storage.
+  // CanUseStorage is called before any DOM initiated operation
+  // on a storage is about to happen and ensures that the storage's
+  // session-only flag is properly set according the current settings.
+  // It is an optimization since the privileges check and session only
+  // state determination are complex and share the code (comes hand in
+  // hand together).
+  bool CanUseStorage(nsIPrincipal& aSubjectPrincipal);
+
+private:
+  ~DOMStorage();
+
+  friend class DOMStorageManager;
+  friend class DOMStorageCache;
+
+  nsCOMPtr<nsPIDOMWindowInner> mWindow;
+  RefPtr<DOMStorageManager> mManager;
+  RefPtr<DOMStorageCache> mCache;
+  nsString mDocumentURI;
+
+  // Principal this DOMStorage (i.e. localStorage or sessionStorage) has
+  // been created for
+  nsCOMPtr<nsIPrincipal> mPrincipal;
+
+  // Whether this storage is running in private-browsing window.
+  bool mIsPrivate : 1;
+
+  // Whether storage is set to persist data only per session, may change
+  // dynamically and is set by CanUseStorage function that is called
+  // before any operation on the storage.
+  bool mIsSessionOnly : 1;
+
+  void BroadcastChangeNotification(const nsSubstring& aKey,
+                                   const nsSubstring& aOldValue,
+                                   const nsSubstring& aNewValue);
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif /* nsDOMStorage_h___ */
diff --git a/dom/storage/DOMStorageCache.cpp b/dom/storage/DOMStorageCache.cpp
new file mode 100644
index 0000000000..811f79fd36
--- /dev/null
+++ b/dom/storage/DOMStorageCache.cpp
@@ -0,0 +1,807 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "DOMStorageCache.h"
+
+#include "DOMStorage.h"
+#include "DOMStorageDBThread.h"
+#include "DOMStorageIPC.h"
+#include "DOMStorageManager.h"
+
+#include "nsAutoPtr.h"
+#include "nsDOMString.h"
+#include "nsXULAppAPI.h"
+#include "mozilla/Unused.h"
+#include "nsProxyRelease.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+namespace dom {
+
+#define DOM_STORAGE_CACHE_KEEP_ALIVE_TIME_MS 20000
+
+// static
+DOMStorageDBBridge* DOMStorageCache::sDatabase = nullptr;
+bool DOMStorageCache::sDatabaseDown = false;
+
+namespace {
+
+const uint32_t kDefaultSet = 0;
+const uint32_t kPrivateSet = 1;
+const uint32_t kSessionSet = 2;
+
+inline uint32_t
+GetDataSetIndex(bool aPrivate, bool aSessionOnly)
+{
+  if (aPrivate) {
+    return kPrivateSet;
+  }
+
+  if (aSessionOnly) {
+    return kSessionSet;
+  }
+
+  return kDefaultSet;
+}
+
+inline uint32_t
+GetDataSetIndex(const DOMStorage* aStorage)
+{
+  return GetDataSetIndex(aStorage->IsPrivate(), aStorage->IsSessionOnly());
+}
+
+} // namespace
+
+// DOMStorageCacheBridge
+
+NS_IMPL_ADDREF(DOMStorageCacheBridge)
+
+// Since there is no consumer of return value of Release, we can turn this 
+// method to void to make implementation of asynchronous DOMStorageCache::Release
+// much simpler.
+NS_IMETHODIMP_(void) DOMStorageCacheBridge::Release(void)
+{
+  MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");
+  nsrefcnt count = --mRefCnt;
+  NS_LOG_RELEASE(this, count, "DOMStorageCacheBridge");
+  if (0 == count) {
+    mRefCnt = 1; /* stabilize */
+    /* enable this to find non-threadsafe destructors: */
+    /* NS_ASSERT_OWNINGTHREAD(_class); */
+    delete (this);
+  }
+}
+
+// DOMStorageCache
+
+DOMStorageCache::DOMStorageCache(const nsACString* aOriginNoSuffix)
+: mOriginNoSuffix(*aOriginNoSuffix)
+, mMonitor("DOMStorageCache")
+, mLoaded(false)
+, mLoadResult(NS_OK)
+, mInitialized(false)
+, mPersistent(false)
+, mSessionOnlyDataSetActive(false)
+, mPreloadTelemetryRecorded(false)
+{
+  MOZ_COUNT_CTOR(DOMStorageCache);
+}
+
+DOMStorageCache::~DOMStorageCache()
+{
+  if (mManager) {
+    mManager->DropCache(this);
+  }
+
+  MOZ_COUNT_DTOR(DOMStorageCache);
+}
+
+NS_IMETHODIMP_(void)
+DOMStorageCache::Release(void)
+{
+  // We must actually release on the main thread since the cache removes it
+  // self from the manager's hash table.  And we don't want to lock access to
+  // that hash table.
+  if (NS_IsMainThread()) {
+    DOMStorageCacheBridge::Release();
+    return;
+  }
+
+  RefPtr<nsRunnableMethod<DOMStorageCacheBridge, void, false> > event =
+    NewNonOwningRunnableMethod(static_cast<DOMStorageCacheBridge*>(this),
+                               &DOMStorageCacheBridge::Release);
+
+  nsresult rv = NS_DispatchToMainThread(event);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("DOMStorageCache::Release() on a non-main thread");
+    DOMStorageCacheBridge::Release();
+  }
+}
+
+void
+DOMStorageCache::Init(DOMStorageManager* aManager,
+                      bool aPersistent,
+                      nsIPrincipal* aPrincipal,
+                      const nsACString& aQuotaOriginScope)
+{
+  if (mInitialized) {
+    return;
+  }
+
+  mInitialized = true;
+  mPrincipal = aPrincipal;
+  BasePrincipal::Cast(aPrincipal)->OriginAttributesRef().CreateSuffix(mOriginSuffix);
+  mPersistent = aPersistent;
+  if (aQuotaOriginScope.IsEmpty()) {
+    mQuotaOriginScope = Origin();
+  } else {
+    mQuotaOriginScope = aQuotaOriginScope;
+  }
+
+  if (mPersistent) {
+    mManager = aManager;
+    Preload();
+  }
+
+  // Check the quota string has (or has not) the identical origin suffix as
+  // this storage cache is bound to.
+  MOZ_ASSERT(StringBeginsWith(mQuotaOriginScope, mOriginSuffix));
+  MOZ_ASSERT(mOriginSuffix.IsEmpty() != StringBeginsWith(mQuotaOriginScope, 
+                                                         NS_LITERAL_CSTRING("^")));
+
+  mUsage = aManager->GetOriginUsage(mQuotaOriginScope);
+}
+
+inline bool
+DOMStorageCache::Persist(const DOMStorage* aStorage) const
+{
+  return mPersistent &&
+         !aStorage->IsSessionOnly() &&
+         !aStorage->IsPrivate();
+}
+
+const nsCString
+DOMStorageCache::Origin() const
+{
+  return DOMStorageManager::CreateOrigin(mOriginSuffix, mOriginNoSuffix);
+}
+
+DOMStorageCache::Data&
+DOMStorageCache::DataSet(const DOMStorage* aStorage)
+{
+  uint32_t index = GetDataSetIndex(aStorage);
+
+  if (index == kSessionSet && !mSessionOnlyDataSetActive) {
+    // Session only data set is demanded but not filled with
+    // current data set, copy to session only set now.
+
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_SESSIONONLY_PRELOAD_BLOCKING_MS);
+
+    Data& defaultSet = mData[kDefaultSet];
+    Data& sessionSet = mData[kSessionSet];
+
+    for (auto iter = defaultSet.mKeys.Iter(); !iter.Done(); iter.Next()) {
+      sessionSet.mKeys.Put(iter.Key(), iter.UserData());
+    }
+
+    mSessionOnlyDataSetActive = true;
+
+    // This updates sessionSet.mOriginQuotaUsage and also updates global usage
+    // for all session only data
+    ProcessUsageDelta(kSessionSet, defaultSet.mOriginQuotaUsage);
+  }
+
+  return mData[index];
+}
+
+bool
+DOMStorageCache::ProcessUsageDelta(const DOMStorage* aStorage, int64_t aDelta)
+{
+  return ProcessUsageDelta(GetDataSetIndex(aStorage), aDelta);
+}
+
+bool
+DOMStorageCache::ProcessUsageDelta(uint32_t aGetDataSetIndex, const int64_t aDelta)
+{
+  // Check if we are in a low disk space situation
+  if (aDelta > 0 && mManager && mManager->IsLowDiskSpace()) {
+    return false;
+  }
+
+  // Check limit per this origin
+  Data& data = mData[aGetDataSetIndex];
+  uint64_t newOriginUsage = data.mOriginQuotaUsage + aDelta;
+  if (aDelta > 0 && newOriginUsage > DOMStorageManager::GetQuota()) {
+    return false;
+  }
+
+  // Now check eTLD+1 limit
+  if (mUsage && !mUsage->CheckAndSetETLD1UsageDelta(aGetDataSetIndex, aDelta)) {
+    return false;
+  }
+
+  // Update size in our data set
+  data.mOriginQuotaUsage = newOriginUsage;
+  return true;
+}
+
+void
+DOMStorageCache::Preload()
+{
+  if (mLoaded || !mPersistent) {
+    return;
+  }
+
+  if (!StartDatabase()) {
+    mLoaded = true;
+    mLoadResult = NS_ERROR_FAILURE;
+    return;
+  }
+
+  sDatabase->AsyncPreload(this);
+}
+
+namespace {
+
+// This class is passed to timer as a tick observer.  It refers the cache
+// and keeps it alive for a time.
+class DOMStorageCacheHolder : public nsITimerCallback
+{
+  virtual ~DOMStorageCacheHolder() {}
+
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD
+  Notify(nsITimer* aTimer) override
+  {
+    mCache = nullptr;
+    return NS_OK;
+  }
+
+  RefPtr<DOMStorageCache> mCache;
+
+public:
+  explicit DOMStorageCacheHolder(DOMStorageCache* aCache) : mCache(aCache) {}
+};
+
+NS_IMPL_ISUPPORTS(DOMStorageCacheHolder, nsITimerCallback)
+
+} // namespace
+
+void
+DOMStorageCache::KeepAlive()
+{
+  // Missing reference back to the manager means the cache is not responsible
+  // for its lifetime.  Used for keeping sessionStorage live forever.
+  if (!mManager) {
+    return;
+  }
+
+  if (!NS_IsMainThread()) {
+    // Timer and the holder must be initialized on the main thread.
+    NS_DispatchToMainThread(NewRunnableMethod(this, &DOMStorageCache::KeepAlive));
+    return;
+  }
+
+  nsCOMPtr<nsITimer> timer = do_CreateInstance("@mozilla.org/timer;1");
+  if (!timer) {
+    return;
+  }
+
+  RefPtr<DOMStorageCacheHolder> holder = new DOMStorageCacheHolder(this);
+  timer->InitWithCallback(holder, DOM_STORAGE_CACHE_KEEP_ALIVE_TIME_MS,
+                          nsITimer::TYPE_ONE_SHOT);
+
+  mKeepAliveTimer.swap(timer);
+}
+
+namespace {
+
+// The AutoTimer provided by telemetry headers is only using static,
+// i.e. compile time known ID, but here we know the ID only at run time.
+// Hence a new class.
+class TelemetryAutoTimer
+{
+public:
+  explicit TelemetryAutoTimer(Telemetry::ID aId)
+    : id(aId), start(TimeStamp::Now()) {}
+  ~TelemetryAutoTimer()
+    { Telemetry::AccumulateDelta_impl<Telemetry::Millisecond>::compute(id, start); }
+private:
+  Telemetry::ID id;
+  const TimeStamp start;
+};
+
+} // namespace
+
+void
+DOMStorageCache::WaitForPreload(Telemetry::ID aTelemetryID)
+{
+  if (!mPersistent) {
+    return;
+  }
+
+  bool loaded = mLoaded;
+
+  // Telemetry of rates of pending preloads
+  if (!mPreloadTelemetryRecorded) {
+    mPreloadTelemetryRecorded = true;
+    Telemetry::Accumulate(
+      Telemetry::LOCALDOMSTORAGE_PRELOAD_PENDING_ON_FIRST_ACCESS,
+      !loaded);
+  }
+
+  if (loaded) {
+    return;
+  }
+
+  // Measure which operation blocks and for how long
+  TelemetryAutoTimer timer(aTelemetryID);
+
+  // If preload already started (i.e. we got some first data, but not all)
+  // SyncPreload will just wait for it to finish rather then synchronously
+  // read from the database.  It seems to me more optimal.
+
+  // TODO place for A/B testing (force main thread load vs. let preload finish)
+
+  // No need to check sDatabase for being non-null since preload is either
+  // done before we've shut the DB down or when the DB could not start,
+  // preload has not even be started.
+  sDatabase->SyncPreload(this);
+}
+
+nsresult
+DOMStorageCache::GetLength(const DOMStorage* aStorage, uint32_t* aRetval)
+{
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_GETLENGTH_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  *aRetval = DataSet(aStorage).mKeys.Count();
+  return NS_OK;
+}
+
+nsresult
+DOMStorageCache::GetKey(const DOMStorage* aStorage, uint32_t aIndex, nsAString& aRetval)
+{
+  // XXX: This does a linear search for the key at index, which would
+  // suck if there's a large numer of indexes. Do we care? If so,
+  // maybe we need to have a lazily populated key array here or
+  // something?
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_GETKEY_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  aRetval.SetIsVoid(true);
+  for (auto iter = DataSet(aStorage).mKeys.Iter(); !iter.Done(); iter.Next()) {
+    if (aIndex == 0) {
+      aRetval = iter.Key();
+      break;
+    }
+    aIndex--;
+  }
+
+  return NS_OK;
+}
+
+void
+DOMStorageCache::GetKeys(const DOMStorage* aStorage, nsTArray<nsString>& aKeys)
+{
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_GETALLKEYS_BLOCKING_MS);
+  }
+
+  if (NS_FAILED(mLoadResult)) {
+    return;
+  }
+
+  for (auto iter = DataSet(aStorage).mKeys.Iter(); !iter.Done(); iter.Next()) {
+    aKeys.AppendElement(iter.Key());
+  }
+}
+
+nsresult
+DOMStorageCache::GetItem(const DOMStorage* aStorage, const nsAString& aKey,
+                         nsAString& aRetval)
+{
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_GETVALUE_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  // not using AutoString since we don't want to copy buffer to result
+  nsString value;
+  if (!DataSet(aStorage).mKeys.Get(aKey, &value)) {
+    SetDOMStringToNull(value);
+  }
+
+  aRetval = value;
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageCache::SetItem(const DOMStorage* aStorage, const nsAString& aKey,
+                         const nsString& aValue, nsString& aOld)
+{
+  // Size of the cache that will change after this action.
+  int64_t delta = 0;
+
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_SETVALUE_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  Data& data = DataSet(aStorage);
+  if (!data.mKeys.Get(aKey, &aOld)) {
+    SetDOMStringToNull(aOld);
+
+    // We only consider key size if the key doesn't exist before.
+    delta += static_cast<int64_t>(aKey.Length());
+  }
+
+  delta += static_cast<int64_t>(aValue.Length()) -
+           static_cast<int64_t>(aOld.Length());
+
+  if (!ProcessUsageDelta(aStorage, delta)) {
+    return NS_ERROR_DOM_QUOTA_REACHED;
+  }
+
+  if (aValue == aOld && DOMStringIsNull(aValue) == DOMStringIsNull(aOld)) {
+    return NS_SUCCESS_DOM_NO_OPERATION;
+  }
+
+  data.mKeys.Put(aKey, aValue);
+
+  if (Persist(aStorage)) {
+    if (!sDatabase) {
+      NS_ERROR("Writing to localStorage after the database has been shut down"
+               ", data lose!");
+      return NS_ERROR_NOT_INITIALIZED;
+    }
+
+    if (DOMStringIsNull(aOld)) {
+      return sDatabase->AsyncAddItem(this, aKey, aValue);
+    }
+
+    return sDatabase->AsyncUpdateItem(this, aKey, aValue);
+  }
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageCache::RemoveItem(const DOMStorage* aStorage, const nsAString& aKey,
+                            nsString& aOld)
+{
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_REMOVEKEY_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  Data& data = DataSet(aStorage);
+  if (!data.mKeys.Get(aKey, &aOld)) {
+    SetDOMStringToNull(aOld);
+    return NS_SUCCESS_DOM_NO_OPERATION;
+  }
+
+  // Recalculate the cached data size
+  const int64_t delta = -(static_cast<int64_t>(aOld.Length()) +
+                          static_cast<int64_t>(aKey.Length()));
+  Unused << ProcessUsageDelta(aStorage, delta);
+  data.mKeys.Remove(aKey);
+
+  if (Persist(aStorage)) {
+    if (!sDatabase) {
+      NS_ERROR("Writing to localStorage after the database has been shut down"
+               ", data lose!");
+      return NS_ERROR_NOT_INITIALIZED;
+    }
+
+    return sDatabase->AsyncRemoveItem(this, aKey);
+  }
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageCache::Clear(const DOMStorage* aStorage)
+{
+  bool refresh = false;
+  if (Persist(aStorage)) {
+    // We need to preload all data (know the size) before we can proceeed
+    // to correctly decrease cached usage number.
+    // XXX as in case of unload, this is not technically needed now, but
+    // after super-scope quota introduction we have to do this.  Get telemetry
+    // right now.
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_CLEAR_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      // When we failed to load data from the database, force delete of the
+      // scope data and make use of the storage possible again.
+      refresh = true;
+      mLoadResult = NS_OK;
+    }
+  }
+
+  Data& data = DataSet(aStorage);
+  bool hadData = !!data.mKeys.Count();
+
+  if (hadData) {
+    Unused << ProcessUsageDelta(aStorage, -data.mOriginQuotaUsage);
+    data.mKeys.Clear();
+  }
+
+  if (Persist(aStorage) && (refresh || hadData)) {
+    if (!sDatabase) {
+      NS_ERROR("Writing to localStorage after the database has been shut down"
+               ", data lose!");
+      return NS_ERROR_NOT_INITIALIZED;
+    }
+
+    return sDatabase->AsyncClear(this);
+  }
+
+  return hadData ? NS_OK : NS_SUCCESS_DOM_NO_OPERATION;
+}
+
+void
+DOMStorageCache::CloneFrom(const DOMStorageCache* aThat)
+{
+  // This will never be called on anything else than SessionStorage.
+  // This means mData will never be touched on any other thread than
+  // the main thread and it never went through the loading process.
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mPersistent);
+  MOZ_ASSERT(!(bool)aThat->mLoaded);
+
+  mLoaded = false;
+  mInitialized = aThat->mInitialized;
+  mPersistent = false;
+  mSessionOnlyDataSetActive = aThat->mSessionOnlyDataSetActive;
+
+  for (uint32_t i = 0; i < kDataSetCount; ++i) {
+    for (auto it = aThat->mData[i].mKeys.ConstIter(); !it.Done(); it.Next()) {
+      mData[i].mKeys.Put(it.Key(), it.UserData());
+    }
+    ProcessUsageDelta(i, aThat->mData[i].mOriginQuotaUsage);
+  }
+}
+
+// Defined in DOMStorageManager.cpp
+extern bool
+PrincipalsEqual(nsIPrincipal* aObjectPrincipal, nsIPrincipal* aSubjectPrincipal);
+
+bool
+DOMStorageCache::CheckPrincipal(nsIPrincipal* aPrincipal) const
+{
+  return PrincipalsEqual(mPrincipal, aPrincipal);
+}
+
+void
+DOMStorageCache::UnloadItems(uint32_t aUnloadFlags)
+{
+  if (aUnloadFlags & kUnloadDefault) {
+    // Must wait for preload to pass correct usage to ProcessUsageDelta
+    // XXX this is not technically needed right now since there is just
+    // per-origin isolated quota handling, but when we introduce super-
+    // -scope quotas, we have to do this.  Better to start getting
+    // telemetry right now.
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_UNLOAD_BLOCKING_MS);
+
+    mData[kDefaultSet].mKeys.Clear();
+    ProcessUsageDelta(kDefaultSet, -mData[kDefaultSet].mOriginQuotaUsage);
+  }
+
+  if (aUnloadFlags & kUnloadPrivate) {
+    mData[kPrivateSet].mKeys.Clear();
+    ProcessUsageDelta(kPrivateSet, -mData[kPrivateSet].mOriginQuotaUsage);
+  }
+
+  if (aUnloadFlags & kUnloadSession) {
+    mData[kSessionSet].mKeys.Clear();
+    ProcessUsageDelta(kSessionSet, -mData[kSessionSet].mOriginQuotaUsage);
+    mSessionOnlyDataSetActive = false;
+  }
+
+#ifdef DOM_STORAGE_TESTS
+  if (aUnloadFlags & kTestReload) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_UNLOAD_BLOCKING_MS);
+
+    mData[kDefaultSet].mKeys.Clear();
+    mLoaded = false; // This is only used in testing code
+    Preload();
+  }
+#endif
+}
+
+// DOMStorageCacheBridge
+
+uint32_t
+DOMStorageCache::LoadedCount()
+{
+  MonitorAutoLock monitor(mMonitor);
+  Data& data = mData[kDefaultSet];
+  return data.mKeys.Count();
+}
+
+bool
+DOMStorageCache::LoadItem(const nsAString& aKey, const nsString& aValue)
+{
+  MonitorAutoLock monitor(mMonitor);
+  if (mLoaded) {
+    return false;
+  }
+
+  Data& data = mData[kDefaultSet];
+  if (data.mKeys.Get(aKey, nullptr)) {
+    return true; // don't stop, just don't override
+  }
+
+  data.mKeys.Put(aKey, aValue);
+  data.mOriginQuotaUsage += aKey.Length() + aValue.Length();
+  return true;
+}
+
+void
+DOMStorageCache::LoadDone(nsresult aRv)
+{
+  // Keep the preloaded cache alive for a time
+  KeepAlive();
+
+  MonitorAutoLock monitor(mMonitor);
+  mLoadResult = aRv;
+  mLoaded = true;
+  monitor.Notify();
+}
+
+void
+DOMStorageCache::LoadWait()
+{
+  MonitorAutoLock monitor(mMonitor);
+  while (!mLoaded) {
+    monitor.Wait();
+  }
+}
+
+// DOMStorageUsage
+
+DOMStorageUsage::DOMStorageUsage(const nsACString& aOriginScope)
+  : mOriginScope(aOriginScope)
+{
+  mUsage[kDefaultSet] = mUsage[kPrivateSet] = mUsage[kSessionSet] = 0LL;
+}
+
+namespace {
+
+class LoadUsageRunnable : public Runnable
+{
+public:
+  LoadUsageRunnable(int64_t* aUsage, const int64_t aDelta)
+    : mTarget(aUsage)
+    , mDelta(aDelta)
+  {}
+
+private:
+  int64_t* mTarget;
+  int64_t mDelta;
+
+  NS_IMETHOD Run() override { *mTarget = mDelta; return NS_OK; }
+};
+
+} // namespace
+
+void
+DOMStorageUsage::LoadUsage(const int64_t aUsage)
+{
+  // Using kDefaultSet index since it is the index for the persitent data
+  // stored in the database we have just loaded usage for.
+  if (!NS_IsMainThread()) {
+    // In single process scenario we get this call from the DB thread
+    RefPtr<LoadUsageRunnable> r =
+      new LoadUsageRunnable(mUsage + kDefaultSet, aUsage);
+    NS_DispatchToMainThread(r);
+  } else {
+    // On a child process we get this on the main thread already
+    mUsage[kDefaultSet] += aUsage;
+  }
+}
+
+bool
+DOMStorageUsage::CheckAndSetETLD1UsageDelta(uint32_t aDataSetIndex, const int64_t aDelta)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  int64_t newUsage = mUsage[aDataSetIndex] + aDelta;
+  if (aDelta > 0 && newUsage > DOMStorageManager::GetQuota()) {
+    return false;
+  }
+
+  mUsage[aDataSetIndex] = newUsage;
+  return true;
+}
+
+
+// static
+DOMStorageDBBridge*
+DOMStorageCache::StartDatabase()
+{
+  if (sDatabase || sDatabaseDown) {
+    // When sDatabaseDown is at true, sDatabase is null.
+    // Checking sDatabaseDown flag here prevents reinitialization of
+    // the database after shutdown.
+    return sDatabase;
+  }
+
+  if (XRE_IsParentProcess()) {
+    nsAutoPtr<DOMStorageDBThread> db(new DOMStorageDBThread());
+
+    nsresult rv = db->Init();
+    if (NS_FAILED(rv)) {
+      return nullptr;
+    }
+
+    sDatabase = db.forget();
+  } else {
+    // Use DOMLocalStorageManager::Ensure in case we're called from
+    // DOMSessionStorageManager's initializer and we haven't yet initialized the
+    // local storage manager.
+    RefPtr<DOMStorageDBChild> db = new DOMStorageDBChild(
+        DOMLocalStorageManager::Ensure());
+
+    nsresult rv = db->Init();
+    if (NS_FAILED(rv)) {
+      return nullptr;
+    }
+
+    db.forget(&sDatabase);
+  }
+
+  return sDatabase;
+}
+
+// static
+DOMStorageDBBridge*
+DOMStorageCache::GetDatabase()
+{
+  return sDatabase;
+}
+
+// static
+nsresult
+DOMStorageCache::StopDatabase()
+{
+  if (!sDatabase) {
+    return NS_OK;
+  }
+
+  sDatabaseDown = true;
+
+  nsresult rv = sDatabase->Shutdown();
+  if (XRE_IsParentProcess()) {
+    delete sDatabase;
+  } else {
+    DOMStorageDBChild* child = static_cast<DOMStorageDBChild*>(sDatabase);
+    NS_RELEASE(child);
+  }
+
+  sDatabase = nullptr;
+  return rv;
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/DOMStorageCache.h b/dom/storage/DOMStorageCache.h
new file mode 100644
index 0000000000..01cf6b3ea5
--- /dev/null
+++ b/dom/storage/DOMStorageCache.h
@@ -0,0 +1,288 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 nsDOMStorageCache_h___
+#define nsDOMStorageCache_h___
+
+#include "nsIPrincipal.h"
+#include "nsITimer.h"
+
+#include "nsString.h"
+#include "nsDataHashtable.h"
+#include "nsHashKeys.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/Atomics.h"
+
+namespace mozilla {
+namespace dom {
+
+class DOMStorage;
+class DOMStorageUsage;
+class DOMStorageManager;
+class DOMStorageDBBridge;
+
+// Interface class on which only the database or IPC may call.
+// Used to populate the cache with DB data.
+class DOMStorageCacheBridge
+{
+public:
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void);
+  NS_IMETHOD_(void) Release(void);
+
+  // The origin of the cache, result is concatenation of OriginNoSuffix() and OriginSuffix(),
+  // see below.
+  virtual const nsCString Origin() const = 0;
+
+  // The origin attributes suffix alone, this is usually passed as an |aOriginSuffix|
+  // argument to various methods
+  virtual const nsCString& OriginSuffix() const = 0;
+
+  // The origin in the database usage format (reversed) and without the suffix
+  virtual const nsCString& OriginNoSuffix() const = 0;
+
+  // Whether the cache is already fully loaded
+  virtual bool Loaded() = 0;
+
+  // How many items has so far been loaded into the cache, used
+  // for optimization purposes
+  virtual uint32_t LoadedCount() = 0;
+
+  // Called by the database to load a key and its value to the cache
+  virtual bool LoadItem(const nsAString& aKey, const nsString& aValue) = 0;
+
+  // Called by the database after all keys and values has been loaded
+  // to this cache
+  virtual void LoadDone(nsresult aRv) = 0;
+
+  // Use to synchronously wait until the cache gets fully loaded with data,
+  // this method exits after LoadDone has been called
+  virtual void LoadWait() = 0;
+
+protected:
+  virtual ~DOMStorageCacheBridge() {}
+
+  ThreadSafeAutoRefCnt mRefCnt;
+  NS_DECL_OWNINGTHREAD
+};
+
+// Implementation of scope cache that is responsible for preloading data
+// for persistent storage (localStorage) and hold data for non-private,
+// private and session-only cookie modes.  It is also responsible for
+// persisting data changes using the database, works as a write-back cache.
+class DOMStorageCache : public DOMStorageCacheBridge
+{
+public:
+  NS_IMETHOD_(void) Release(void);
+
+  // Note: We pass aOriginNoSuffix through the ctor here, because 
+  // DOMStorageCacheHashKey's ctor is creating this class and 
+  // accepts reversed-origin-no-suffix as an argument - the hashing key.
+  explicit DOMStorageCache(const nsACString* aOriginNoSuffix);
+
+protected:
+  virtual ~DOMStorageCache();
+
+public:
+  void Init(DOMStorageManager* aManager, bool aPersistent, nsIPrincipal* aPrincipal,
+            const nsACString& aQuotaOriginScope);
+
+  // Copies all data from the other storage.
+  void CloneFrom(const DOMStorageCache* aThat);
+
+  // Starts async preload of this cache if it persistent and not loaded.
+  void Preload();
+
+  // Keeps the cache alive (i.e. present in the manager's hash table) for a time.
+  void KeepAlive();
+
+  // The set of methods that are invoked by DOM storage web API.
+  // We are passing the DOMStorage object just to let the cache
+  // read properties like mPrivate, mPrincipal and mSessionOnly.
+  // Get* methods return error when load from the database has failed.
+  nsresult GetLength(const DOMStorage* aStorage, uint32_t* aRetval);
+  nsresult GetKey(const DOMStorage* aStorage, uint32_t index, nsAString& aRetval);
+  nsresult GetItem(const DOMStorage* aStorage, const nsAString& aKey, nsAString& aRetval);
+  nsresult SetItem(const DOMStorage* aStorage, const nsAString& aKey, const nsString& aValue, nsString& aOld);
+  nsresult RemoveItem(const DOMStorage* aStorage, const nsAString& aKey, nsString& aOld);
+  nsresult Clear(const DOMStorage* aStorage);
+
+  void GetKeys(const DOMStorage* aStorage, nsTArray<nsString>& aKeys);
+
+  // Whether the principal equals principal the cache was created for
+  bool CheckPrincipal(nsIPrincipal* aPrincipal) const;
+  nsIPrincipal* Principal() const { return mPrincipal; }
+
+  // Starts the database engine thread or the IPC bridge
+  static DOMStorageDBBridge* StartDatabase();
+  static DOMStorageDBBridge* GetDatabase();
+
+  // Stops the thread and flushes all uncommited data
+  static nsresult StopDatabase();
+
+  // DOMStorageCacheBridge
+
+  virtual const nsCString Origin() const;
+  virtual const nsCString& OriginNoSuffix() const { return mOriginNoSuffix; }
+  virtual const nsCString& OriginSuffix() const { return mOriginSuffix; }
+  virtual bool Loaded() { return mLoaded; }
+  virtual uint32_t LoadedCount();
+  virtual bool LoadItem(const nsAString& aKey, const nsString& aValue);
+  virtual void LoadDone(nsresult aRv);
+  virtual void LoadWait();
+
+  // Cache keeps 3 sets of data: regular, private and session-only.
+  // This class keeps keys and values for a set and also caches
+  // size of the data for quick per-origin quota checking.
+  class Data
+  {
+  public:
+    Data() : mOriginQuotaUsage(0) {}
+    int64_t mOriginQuotaUsage;
+    nsDataHashtable<nsStringHashKey, nsString> mKeys;
+  };
+
+public:
+  // Number of data sets we keep: default, private, session
+  static const uint32_t kDataSetCount = 3;
+
+private:
+  // API to clear the cache data, this is invoked by chrome operations
+  // like cookie deletion.
+  friend class DOMStorageManager;
+
+  static const uint32_t kUnloadDefault = 1 << 0;
+  static const uint32_t kUnloadPrivate = 1 << 1;
+  static const uint32_t kUnloadSession = 1 << 2;
+  static const uint32_t kUnloadComplete =
+    kUnloadDefault | kUnloadPrivate | kUnloadSession;
+
+#ifdef DOM_STORAGE_TESTS
+  static const uint32_t kTestReload    = 1 << 15;
+#endif
+
+  void UnloadItems(uint32_t aUnloadFlags);
+
+private:
+  // Synchronously blocks until the cache is fully loaded from the database
+  void WaitForPreload(mozilla::Telemetry::ID aTelemetryID);
+
+  // Helper to get one of the 3 data sets (regular, private, session)
+  Data& DataSet(const DOMStorage* aStorage);
+
+  // Whether the storage change is about to persist
+  bool Persist(const DOMStorage* aStorage) const;
+
+  // Changes the quota usage on the given data set if it fits the quota.
+  // If not, then false is returned and no change to the set must be done.
+  bool ProcessUsageDelta(uint32_t aGetDataSetIndex, const int64_t aDelta);
+  bool ProcessUsageDelta(const DOMStorage* aStorage, const int64_t aDelta);
+
+private:
+  // When a cache is reponsible for its life time (in case of localStorage data
+  // cache) we need to refer our manager since removal of the cache from the hash
+  // table is handled in the destructor by call to the manager.
+  // Cache could potentially overlive the manager, hence the hard ref.
+  RefPtr<DOMStorageManager> mManager;
+
+  // Reference to the usage counter object we check on for eTLD+1 quota limit.
+  // Obtained from the manager during initialization (Init method).
+  RefPtr<DOMStorageUsage> mUsage;
+
+  // Timer that holds this cache alive for a while after it has been preloaded.
+  nsCOMPtr<nsITimer> mKeepAliveTimer;
+
+  // Principal the cache has been initially created for, this is used only
+  // for sessionStorage access checks since sessionStorage objects are strictly
+  // scoped by a principal.  localStorage objects on the other hand are scoped by
+  // origin only.
+  nsCOMPtr<nsIPrincipal> mPrincipal;
+
+  // The origin this cache belongs to in the "DB format", i.e. reversed
+  nsCString mOriginNoSuffix;
+
+  // The origin attributes suffix
+  nsCString mOriginSuffix;
+
+  // The eTLD+1 scope used to count quota usage.  It is in the reversed format 
+  // and contains the origin attributes suffix.
+  nsCString mQuotaOriginScope;
+
+  // Non-private Browsing, Private Browsing and Session Only sets.
+  Data mData[kDataSetCount];
+
+  // This monitor is used to wait for full load of data.
+  mozilla::Monitor mMonitor;
+
+  // Flag that is initially false.  When the cache is about to work with
+  // the database (i.e. it is persistent) this flags is set to true after
+  // all keys and coresponding values are loaded from the database.
+  // This flag never goes from true back to false.  Since this flag is
+  // critical for mData hashtable synchronization, it's made atomic.
+  Atomic<bool, ReleaseAcquire> mLoaded;
+
+  // Result of load from the database.  Valid after mLoaded flag has been set.
+  nsresult mLoadResult;
+
+  // Init() method has been called
+  bool mInitialized : 1;
+
+  // This cache is about to be bound with the database (i.e. it has
+  // to load from the DB first and has to persist when modifying the
+  // default data set.)
+  bool mPersistent : 1;
+
+  // - False when the session-only data set was never used.
+  // - True after access to session-only data has been made for the first time.
+  // We also fill session-only data set with the default one at that moment.
+  // Drops back to false when session-only data are cleared from chrome.
+  bool mSessionOnlyDataSetActive : 1;
+
+  // Whether we have already captured state of the cache preload on our first access.
+  bool mPreloadTelemetryRecorded : 1;
+
+  // DOMStorageDBThread on the parent or single process,
+  // DOMStorageDBChild on the child process.
+  static DOMStorageDBBridge* sDatabase;
+
+  // False until we shut the database down.
+  static bool sDatabaseDown;
+};
+
+// DOMStorageUsage
+// Infrastructure to manage and check eTLD+1 quota
+class DOMStorageUsageBridge
+{
+public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(DOMStorageUsageBridge)
+
+  virtual const nsCString& OriginScope() = 0;
+  virtual void LoadUsage(const int64_t aUsage) = 0;
+
+protected:
+  // Protected destructor, to discourage deletion outside of Release():
+  virtual ~DOMStorageUsageBridge() {}
+};
+
+class DOMStorageUsage : public DOMStorageUsageBridge
+{
+public:
+  explicit DOMStorageUsage(const nsACString& aOriginScope);
+
+  bool CheckAndSetETLD1UsageDelta(uint32_t aDataSetIndex, int64_t aUsageDelta);
+
+private:
+  virtual const nsCString& OriginScope() { return mOriginScope; }
+  virtual void LoadUsage(const int64_t aUsage);
+
+  nsCString mOriginScope;
+  int64_t mUsage[DOMStorageCache::kDataSetCount];
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif
diff --git a/dom/storage/DOMStorageDBThread.cpp b/dom/storage/DOMStorageDBThread.cpp
new file mode 100644
index 0000000000..183be5c5c8
--- /dev/null
+++ b/dom/storage/DOMStorageDBThread.cpp
@@ -0,0 +1,1486 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "DOMStorageDBThread.h"
+#include "DOMStorageDBUpdater.h"
+#include "DOMStorageCache.h"
+#include "DOMStorageManager.h"
+
+#include "nsIEffectiveTLDService.h"
+#include "nsDirectoryServiceUtils.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsThreadUtils.h"
+#include "nsProxyRelease.h"
+#include "mozStorageCID.h"
+#include "mozStorageHelper.h"
+#include "mozIStorageService.h"
+#include "mozIStorageBindingParamsArray.h"
+#include "mozIStorageBindingParams.h"
+#include "mozIStorageValueArray.h"
+#include "mozIStorageFunction.h"
+#include "mozilla/BasePrincipal.h"
+#include "nsIObserverService.h"
+#include "nsVariant.h"
+#include "mozilla/IOInterposer.h"
+#include "mozilla/Services.h"
+#include "mozilla/Tokenizer.h"
+
+// How long we collect write oprerations
+// before they are flushed to the database
+// In milliseconds.
+#define FLUSHING_INTERVAL_MS 5000
+
+// Write Ahead Log's maximum size is 512KB
+#define MAX_WAL_SIZE_BYTES 512 * 1024
+
+// Current version of the database schema
+#define CURRENT_SCHEMA_VERSION 1
+
+namespace mozilla {
+namespace dom {
+
+namespace { // anon
+
+// This is only a compatibility code for schema version 0.  Returns the 'scope' key
+// in the schema version 0 format for the scope column.
+nsCString
+Scheme0Scope(DOMStorageCacheBridge* aCache)
+{
+  nsCString result;
+
+  nsCString suffix = aCache->OriginSuffix();
+
+  PrincipalOriginAttributes oa;
+  if (!suffix.IsEmpty()) {
+    DebugOnly<bool> success = oa.PopulateFromSuffix(suffix);
+    MOZ_ASSERT(success);
+  }
+
+  if (oa.mAppId != nsIScriptSecurityManager::NO_APP_ID || oa.mInIsolatedMozBrowser) {
+    result.AppendInt(oa.mAppId);
+    result.Append(':');
+    result.Append(oa.mInIsolatedMozBrowser ? 't' : 'f');
+    result.Append(':');
+  }
+
+  // If there is more than just appid and/or inbrowser stored in origin
+  // attributes, put it to the schema 0 scope as well.  We must do that
+  // to keep the scope column unique (same resolution as schema 1 has
+  // with originAttributes and originKey columns) so that switch between
+  // schema 1 and 0 always works in both ways.
+  nsAutoCString remaining;
+  oa.mAppId = 0;
+  oa.mInIsolatedMozBrowser = false;
+  oa.CreateSuffix(remaining);
+  if (!remaining.IsEmpty()) {
+    MOZ_ASSERT(!suffix.IsEmpty());
+
+    if (result.IsEmpty()) {
+      // Must contain the old prefix, otherwise we won't search for the whole
+      // origin attributes suffix.
+      result.Append(NS_LITERAL_CSTRING("0:f:"));
+    }
+    // Append the whole origin attributes suffix despite we have already stored
+    // appid and inbrowser.  We are only looking for it when the scope string
+    // starts with "$appid:$inbrowser:" (with whatever valid values).
+    //
+    // The OriginAttributes suffix is a string in a form like:
+    // "^addonId=101&userContextId=5" and it's ensured it always starts with '^'
+    // and never contains ':'.  See OriginAttributes::CreateSuffix.
+    result.Append(suffix);
+    result.Append(':');
+  }
+
+  result.Append(aCache->OriginNoSuffix());
+
+  return result;
+}
+
+} // anon
+
+
+DOMStorageDBBridge::DOMStorageDBBridge()
+{
+}
+
+
+DOMStorageDBThread::DOMStorageDBThread()
+: mThread(nullptr)
+, mThreadObserver(new ThreadObserver())
+, mStopIOThread(false)
+, mWALModeEnabled(false)
+, mDBReady(false)
+, mStatus(NS_OK)
+, mWorkerStatements(mWorkerConnection)
+, mReaderStatements(mReaderConnection)
+, mDirtyEpoch(0)
+, mFlushImmediately(false)
+, mPriorityCounter(0)
+{
+}
+
+nsresult
+DOMStorageDBThread::Init()
+{
+  nsresult rv;
+
+  // Need to determine location on the main thread, since
+  // NS_GetSpecialDirectory access the atom table that can
+  // be accessed only on the main thread.
+  rv = NS_GetSpecialDirectory(NS_APP_USER_PROFILE_50_DIR,
+                              getter_AddRefs(mDatabaseFile));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = mDatabaseFile->Append(NS_LITERAL_STRING("webappsstore.sqlite"));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Ensure mozIStorageService init on the main thread first.
+  nsCOMPtr<mozIStorageService> service =
+    do_GetService(MOZ_STORAGE_SERVICE_CONTRACTID, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Need to keep the lock to avoid setting mThread later then
+  // the thread body executes.
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+
+  mThread = PR_CreateThread(PR_USER_THREAD, &DOMStorageDBThread::ThreadFunc, this,
+                            PR_PRIORITY_LOW, PR_GLOBAL_THREAD, PR_JOINABLE_THREAD,
+                            262144);
+  if (!mThread) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBThread::Shutdown()
+{
+  if (!mThread) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  Telemetry::AutoTimer<Telemetry::LOCALDOMSTORAGE_SHUTDOWN_DATABASE_MS> timer;
+
+  {
+    MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+
+    // After we stop, no other operations can be accepted
+    mFlushImmediately = true;
+    mStopIOThread = true;
+    monitor.Notify();
+  }
+
+  PR_JoinThread(mThread);
+  mThread = nullptr;
+
+  return mStatus;
+}
+
+void
+DOMStorageDBThread::SyncPreload(DOMStorageCacheBridge* aCache, bool aForceSync)
+{
+  PROFILER_LABEL_FUNC(js::ProfileEntry::Category::STORAGE);
+  if (!aForceSync && aCache->LoadedCount()) {
+    // Preload already started for this cache, just wait for it to finish.
+    // LoadWait will exit after LoadDone on the cache has been called.
+    SetHigherPriority();
+    aCache->LoadWait();
+    SetDefaultPriority();
+    return;
+  }
+
+  // Bypass sync load when an update is pending in the queue to write, we would
+  // get incosistent data in the cache.  Also don't allow sync main-thread preload
+  // when DB open and init is still pending on the background thread.
+  if (mDBReady && mWALModeEnabled) {
+    bool pendingTasks;
+    {
+      MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+      pendingTasks = mPendingTasks.IsOriginUpdatePending(aCache->OriginSuffix(), aCache->OriginNoSuffix()) ||
+                     mPendingTasks.IsOriginClearPending(aCache->OriginSuffix(), aCache->OriginNoSuffix());
+    }
+
+    if (!pendingTasks) {
+      // WAL is enabled, thus do the load synchronously on the main thread.
+      DBOperation preload(DBOperation::opPreload, aCache);
+      preload.PerformAndFinalize(this);
+      return;
+    }
+  }
+
+  // Need to go asynchronously since WAL is not allowed or scheduled updates
+  // need to be flushed first.
+  // Schedule preload for this cache as the first operation.
+  nsresult rv = InsertDBOp(new DBOperation(DBOperation::opPreloadUrgent, aCache));
+
+  // LoadWait exits after LoadDone of the cache has been called.
+  if (NS_SUCCEEDED(rv)) {
+    aCache->LoadWait();
+  }
+}
+
+void
+DOMStorageDBThread::AsyncFlush()
+{
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+  mFlushImmediately = true;
+  monitor.Notify();
+}
+
+bool
+DOMStorageDBThread::ShouldPreloadOrigin(const nsACString& aOrigin)
+{
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+  return mOriginsHavingData.Contains(aOrigin);
+}
+
+void
+DOMStorageDBThread::GetOriginsHavingData(InfallibleTArray<nsCString>* aOrigins)
+{
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+  for (auto iter = mOriginsHavingData.Iter(); !iter.Done(); iter.Next()) {
+    aOrigins->AppendElement(iter.Get()->GetKey());
+  }
+}
+
+nsresult
+DOMStorageDBThread::InsertDBOp(DOMStorageDBThread::DBOperation* aOperation)
+{
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+
+  // Sentinel to don't forget to delete the operation when we exit early.
+  nsAutoPtr<DOMStorageDBThread::DBOperation> opScope(aOperation);
+
+  if (NS_FAILED(mStatus)) {
+    MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
+    aOperation->Finalize(mStatus);
+    return mStatus;
+  }
+
+  if (mStopIOThread) {
+    // Thread use after shutdown demanded.
+    MOZ_ASSERT(false);
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  switch (aOperation->Type()) {
+  case DBOperation::opPreload:
+  case DBOperation::opPreloadUrgent:
+    if (mPendingTasks.IsOriginUpdatePending(aOperation->OriginSuffix(), aOperation->OriginNoSuffix())) {
+      // If there is a pending update operation for the scope first do the flush
+      // before we preload the cache.  This may happen in an extremely rare case
+      // when a child process throws away its cache before flush on the parent
+      // has finished.  If we would preloaded the cache as a priority operation 
+      // before the pending flush, we would have got an inconsistent cache content.
+      mFlushImmediately = true;
+    } else if (mPendingTasks.IsOriginClearPending(aOperation->OriginSuffix(), aOperation->OriginNoSuffix())) {
+      // The scope is scheduled to be cleared, so just quickly load as empty.
+      // We need to do this to prevent load of the DB data before the scope has
+      // actually been cleared from the database.  Preloads are processed
+      // immediately before update and clear operations on the database that
+      // are flushed periodically in batches.
+      MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
+      aOperation->Finalize(NS_OK);
+      return NS_OK;
+    }
+    MOZ_FALLTHROUGH;
+
+  case DBOperation::opGetUsage:
+    if (aOperation->Type() == DBOperation::opPreloadUrgent) {
+      SetHigherPriority(); // Dropped back after urgent preload execution
+      mPreloads.InsertElementAt(0, aOperation);
+    } else {
+      mPreloads.AppendElement(aOperation);
+    }
+
+    // DB operation adopted, don't delete it.
+    opScope.forget();
+
+    // Immediately start executing this.
+    monitor.Notify();
+    break;
+
+  default:
+    // Update operations are first collected, coalesced and then flushed
+    // after a short time.
+    mPendingTasks.Add(aOperation);
+
+    // DB operation adopted, don't delete it.
+    opScope.forget();
+
+    ScheduleFlush();
+    break;
+  }
+
+  return NS_OK;
+}
+
+void
+DOMStorageDBThread::SetHigherPriority()
+{
+  ++mPriorityCounter;
+  PR_SetThreadPriority(mThread, PR_PRIORITY_URGENT);
+}
+
+void
+DOMStorageDBThread::SetDefaultPriority()
+{
+  if (--mPriorityCounter <= 0) {
+    PR_SetThreadPriority(mThread, PR_PRIORITY_LOW);
+  }
+}
+
+void
+DOMStorageDBThread::ThreadFunc(void* aArg)
+{
+  PR_SetCurrentThreadName("localStorage DB");
+  mozilla::IOInterposer::RegisterCurrentThread();
+
+  DOMStorageDBThread* thread = static_cast<DOMStorageDBThread*>(aArg);
+  thread->ThreadFunc();
+  mozilla::IOInterposer::UnregisterCurrentThread();
+}
+
+void
+DOMStorageDBThread::ThreadFunc()
+{
+  nsresult rv = InitDatabase();
+
+  MonitorAutoLock lockMonitor(mThreadObserver->GetMonitor());
+
+  if (NS_FAILED(rv)) {
+    mStatus = rv;
+    mStopIOThread = true;
+    return;
+  }
+
+  // Create an nsIThread for the current PRThread, so we can observe runnables
+  // dispatched to it.
+  nsCOMPtr<nsIThread> thread = NS_GetCurrentThread();
+  nsCOMPtr<nsIThreadInternal> threadInternal = do_QueryInterface(thread);
+  MOZ_ASSERT(threadInternal); // Should always succeed.
+  threadInternal->SetObserver(mThreadObserver);
+
+  while (MOZ_LIKELY(!mStopIOThread || mPreloads.Length() ||
+                    mPendingTasks.HasTasks() ||
+                    mThreadObserver->HasPendingEvents())) {
+    // Process xpcom events first.
+    while (MOZ_UNLIKELY(mThreadObserver->HasPendingEvents())) {
+      mThreadObserver->ClearPendingEvents();
+      MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
+      bool processedEvent;
+      do {
+        rv = thread->ProcessNextEvent(false, &processedEvent);
+      } while (NS_SUCCEEDED(rv) && processedEvent);
+    }
+
+    if (MOZ_UNLIKELY(TimeUntilFlush() == 0)) {
+      // Flush time is up or flush has been forced, do it now.
+      UnscheduleFlush();
+      if (mPendingTasks.Prepare()) {
+        {
+          MonitorAutoUnlock unlockMonitor(mThreadObserver->GetMonitor());
+          rv = mPendingTasks.Execute(this);
+        }
+
+        if (!mPendingTasks.Finalize(rv)) {
+          mStatus = rv;
+          NS_WARNING("localStorage DB access broken");
+        }
+      }
+      NotifyFlushCompletion();
+    } else if (MOZ_LIKELY(mPreloads.Length())) {
+      nsAutoPtr<DBOperation> op(mPreloads[0]);
+      mPreloads.RemoveElementAt(0);
+      {
+        MonitorAutoUnlock unlockMonitor(mThreadObserver->GetMonitor());
+        op->PerformAndFinalize(this);
+      }
+
+      if (op->Type() == DBOperation::opPreloadUrgent) {
+        SetDefaultPriority(); // urgent preload unscheduled
+      }
+    } else if (MOZ_UNLIKELY(!mStopIOThread)) {
+      lockMonitor.Wait(TimeUntilFlush());
+    }
+  } // thread loop
+
+  mStatus = ShutdownDatabase();
+
+  if (threadInternal) {
+    threadInternal->SetObserver(nullptr);
+  }
+}
+
+
+NS_IMPL_ISUPPORTS(DOMStorageDBThread::ThreadObserver, nsIThreadObserver)
+
+NS_IMETHODIMP
+DOMStorageDBThread::ThreadObserver::OnDispatchedEvent(nsIThreadInternal *thread)
+{
+  MonitorAutoLock lock(mMonitor);
+  mHasPendingEvents = true;
+  lock.Notify();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+DOMStorageDBThread::ThreadObserver::OnProcessNextEvent(nsIThreadInternal *thread,
+                                       bool mayWait)
+{
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+DOMStorageDBThread::ThreadObserver::AfterProcessNextEvent(nsIThreadInternal *thread,
+                                          bool eventWasProcessed)
+{
+  return NS_OK;
+}
+
+
+extern void
+ReverseString(const nsCSubstring& aSource, nsCSubstring& aResult);
+
+nsresult
+DOMStorageDBThread::OpenDatabaseConnection()
+{
+  nsresult rv;
+
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  nsCOMPtr<mozIStorageService> service
+      = do_GetService(MOZ_STORAGE_SERVICE_CONTRACTID, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = service->OpenUnsharedDatabase(mDatabaseFile, getter_AddRefs(mWorkerConnection));
+  if (rv == NS_ERROR_FILE_CORRUPTED) {
+    // delete the db and try opening again
+    rv = mDatabaseFile->Remove(false);
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = service->OpenUnsharedDatabase(mDatabaseFile, getter_AddRefs(mWorkerConnection));
+  }
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBThread::OpenAndUpdateDatabase()
+{
+  nsresult rv;
+
+  // Here we are on the worker thread. This opens the worker connection.
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  rv = OpenDatabaseConnection();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = TryJournalMode();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBThread::InitDatabase()
+{
+  nsresult rv;
+
+  // Here we are on the worker thread. This opens the worker connection.
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  rv = OpenAndUpdateDatabase();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = DOMStorageDBUpdater::Update(mWorkerConnection);
+  if (NS_FAILED(rv)) {
+    // Update has failed, rather throw the database away and try
+    // opening and setting it up again.
+    rv = mWorkerConnection->Close();
+    mWorkerConnection = nullptr;
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = mDatabaseFile->Remove(false);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = OpenAndUpdateDatabase();
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // Create a read-only clone
+  (void)mWorkerConnection->Clone(true, getter_AddRefs(mReaderConnection));
+  NS_ENSURE_TRUE(mReaderConnection, NS_ERROR_FAILURE);
+
+  // Database open and all initiation operation are done.  Switching this flag
+  // to true allow main thread to read directly from the database.
+  // If we would allow this sooner, we would have opened a window where main thread
+  // read might operate on a totaly broken and incosistent database.
+  mDBReady = true;
+
+  // List scopes having any stored data
+  nsCOMPtr<mozIStorageStatement> stmt;
+  // Note: result of this select must match DOMStorageManager::CreateOrigin()
+  rv = mWorkerConnection->CreateStatement(NS_LITERAL_CSTRING(
+        "SELECT DISTINCT originAttributes || ':' || originKey FROM webappsstore2"),
+        getter_AddRefs(stmt));
+  NS_ENSURE_SUCCESS(rv, rv);
+  mozStorageStatementScoper scope(stmt);
+
+  bool exists;
+  while (NS_SUCCEEDED(rv = stmt->ExecuteStep(&exists)) && exists) {
+    nsAutoCString foundOrigin;
+    rv = stmt->GetUTF8String(0, foundOrigin);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+    mOriginsHavingData.PutEntry(foundOrigin);
+  }
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBThread::SetJournalMode(bool aIsWal)
+{
+  nsresult rv;
+
+  nsAutoCString stmtString(
+    MOZ_STORAGE_UNIQUIFY_QUERY_STR "PRAGMA journal_mode = ");
+  if (aIsWal) {
+    stmtString.AppendLiteral("wal");
+  } else {
+    stmtString.AppendLiteral("truncate");
+  }
+
+  nsCOMPtr<mozIStorageStatement> stmt;
+  rv = mWorkerConnection->CreateStatement(stmtString, getter_AddRefs(stmt));
+  NS_ENSURE_SUCCESS(rv, rv);
+  mozStorageStatementScoper scope(stmt);
+
+  bool hasResult = false;
+  rv = stmt->ExecuteStep(&hasResult);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if (!hasResult) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoCString journalMode;
+  rv = stmt->GetUTF8String(0, journalMode);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if ((aIsWal && !journalMode.EqualsLiteral("wal")) ||
+      (!aIsWal && !journalMode.EqualsLiteral("truncate"))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBThread::TryJournalMode()
+{
+  nsresult rv;
+
+  rv = SetJournalMode(true);
+  if (NS_FAILED(rv)) {
+    mWALModeEnabled = false;
+
+    rv = SetJournalMode(false);
+    NS_ENSURE_SUCCESS(rv, rv);
+  } else {
+    mWALModeEnabled = true;
+
+    rv = ConfigureWALBehavior();
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBThread::ConfigureWALBehavior()
+{
+  // Get the DB's page size
+  nsCOMPtr<mozIStorageStatement> stmt;
+  nsresult rv = mWorkerConnection->CreateStatement(NS_LITERAL_CSTRING(
+    MOZ_STORAGE_UNIQUIFY_QUERY_STR "PRAGMA page_size"
+  ), getter_AddRefs(stmt));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  bool hasResult = false;
+  rv = stmt->ExecuteStep(&hasResult);
+  NS_ENSURE_TRUE(NS_SUCCEEDED(rv) && hasResult, NS_ERROR_FAILURE);
+
+  int32_t pageSize = 0;
+  rv = stmt->GetInt32(0, &pageSize);
+  NS_ENSURE_TRUE(NS_SUCCEEDED(rv) && pageSize > 0, NS_ERROR_UNEXPECTED);
+
+  // Set the threshold for auto-checkpointing the WAL.
+  // We don't want giant logs slowing down reads & shutdown.
+  int32_t thresholdInPages = static_cast<int32_t>(MAX_WAL_SIZE_BYTES / pageSize);
+  nsAutoCString thresholdPragma("PRAGMA wal_autocheckpoint = ");
+  thresholdPragma.AppendInt(thresholdInPages);
+  rv = mWorkerConnection->ExecuteSimpleSQL(thresholdPragma);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Set the maximum WAL log size to reduce footprint on mobile (large empty
+  // WAL files will be truncated)
+  nsAutoCString journalSizePragma("PRAGMA journal_size_limit = ");
+  // bug 600307: mak recommends setting this to 3 times the auto-checkpoint threshold
+  journalSizePragma.AppendInt(MAX_WAL_SIZE_BYTES * 3);
+  rv = mWorkerConnection->ExecuteSimpleSQL(journalSizePragma);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBThread::ShutdownDatabase()
+{
+  // Has to be called on the worker thread.
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  nsresult rv = mStatus;
+
+  mDBReady = false;
+
+  // Finalize the cached statements.
+  mReaderStatements.FinalizeStatements();
+  mWorkerStatements.FinalizeStatements();
+
+  if (mReaderConnection) {
+    // No need to sync access to mReaderConnection since the main thread
+    // is right now joining this thread, unable to execute any events.
+    mReaderConnection->Close();
+    mReaderConnection = nullptr;
+  }
+
+  if (mWorkerConnection) {
+    rv = mWorkerConnection->Close();
+    mWorkerConnection = nullptr;
+  }
+
+  return rv;
+}
+
+void
+DOMStorageDBThread::ScheduleFlush()
+{
+  if (mDirtyEpoch) {
+    return; // Already scheduled
+  }
+
+  mDirtyEpoch = PR_IntervalNow() | 1; // Must be non-zero to indicate we are scheduled
+
+  // Wake the monitor from indefinite sleep...
+  (mThreadObserver->GetMonitor()).Notify();
+}
+
+void
+DOMStorageDBThread::UnscheduleFlush()
+{
+  // We are just about to do the flush, drop flags
+  mFlushImmediately = false;
+  mDirtyEpoch = 0;
+}
+
+PRIntervalTime
+DOMStorageDBThread::TimeUntilFlush()
+{
+  if (mFlushImmediately) {
+    return 0; // Do it now regardless the timeout.
+  }
+
+  static_assert(PR_INTERVAL_NO_TIMEOUT != 0,
+      "PR_INTERVAL_NO_TIMEOUT must be non-zero");
+
+  if (!mDirtyEpoch) {
+    return PR_INTERVAL_NO_TIMEOUT; // No pending task...
+  }
+
+  static const PRIntervalTime kMaxAge = PR_MillisecondsToInterval(FLUSHING_INTERVAL_MS);
+
+  PRIntervalTime now = PR_IntervalNow() | 1;
+  PRIntervalTime age = now - mDirtyEpoch;
+  if (age > kMaxAge) {
+    return 0; // It is time.
+  }
+
+  return kMaxAge - age; // Time left, this is used to sleep the monitor
+}
+
+void
+DOMStorageDBThread::NotifyFlushCompletion()
+{
+#ifdef DOM_STORAGE_TESTS
+  if (!NS_IsMainThread()) {
+    RefPtr<nsRunnableMethod<DOMStorageDBThread, void, false> > event =
+      NewNonOwningRunnableMethod(this, &DOMStorageDBThread::NotifyFlushCompletion);
+    NS_DispatchToMainThread(event);
+    return;
+  }
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->NotifyObservers(nullptr, "domstorage-test-flushed", nullptr);
+  }
+#endif
+}
+
+// Helper SQL function classes
+
+namespace {
+
+class OriginAttrsPatternMatchSQLFunction final : public mozIStorageFunction
+{
+  NS_DECL_ISUPPORTS
+  NS_DECL_MOZISTORAGEFUNCTION
+
+  explicit OriginAttrsPatternMatchSQLFunction(OriginAttributesPattern const& aPattern)
+    : mPattern(aPattern) {}
+
+private:
+  OriginAttrsPatternMatchSQLFunction() = delete;
+  ~OriginAttrsPatternMatchSQLFunction() {}
+
+  OriginAttributesPattern mPattern;
+};
+
+NS_IMPL_ISUPPORTS(OriginAttrsPatternMatchSQLFunction, mozIStorageFunction)
+
+NS_IMETHODIMP
+OriginAttrsPatternMatchSQLFunction::OnFunctionCall(
+    mozIStorageValueArray* aFunctionArguments, nsIVariant** aResult)
+{
+  nsresult rv;
+
+  nsAutoCString suffix;
+  rv = aFunctionArguments->GetUTF8String(0, suffix);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  PrincipalOriginAttributes oa;
+  bool success = oa.PopulateFromSuffix(suffix);
+  NS_ENSURE_TRUE(success, NS_ERROR_FAILURE);
+  bool result = mPattern.Matches(oa);
+
+  RefPtr<nsVariant> outVar(new nsVariant());
+  rv = outVar->SetAsBool(result);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  outVar.forget(aResult);
+  return NS_OK;
+}
+
+} // namespace
+
+// DOMStorageDBThread::DBOperation
+
+DOMStorageDBThread::DBOperation::DBOperation(const OperationType aType,
+                                             DOMStorageCacheBridge* aCache,
+                                             const nsAString& aKey,
+                                             const nsAString& aValue)
+: mType(aType)
+, mCache(aCache)
+, mKey(aKey)
+, mValue(aValue)
+{
+  MOZ_ASSERT(mType == opPreload ||
+             mType == opPreloadUrgent ||
+             mType == opAddItem ||
+             mType == opUpdateItem ||
+             mType == opRemoveItem ||
+             mType == opClear ||
+             mType == opClearAll);
+  MOZ_COUNT_CTOR(DOMStorageDBThread::DBOperation);
+}
+
+DOMStorageDBThread::DBOperation::DBOperation(const OperationType aType,
+                                             DOMStorageUsageBridge* aUsage)
+: mType(aType)
+, mUsage(aUsage)
+{
+  MOZ_ASSERT(mType == opGetUsage);
+  MOZ_COUNT_CTOR(DOMStorageDBThread::DBOperation);
+}
+
+DOMStorageDBThread::DBOperation::DBOperation(const OperationType aType,
+                                             const nsACString& aOriginNoSuffix)
+: mType(aType)
+, mCache(nullptr)
+, mOrigin(aOriginNoSuffix)
+{
+  MOZ_ASSERT(mType == opClearMatchingOrigin);
+  MOZ_COUNT_CTOR(DOMStorageDBThread::DBOperation);
+}
+
+DOMStorageDBThread::DBOperation::DBOperation(const OperationType aType,
+                                             const OriginAttributesPattern& aOriginNoSuffix)
+: mType(aType)
+, mCache(nullptr)
+, mOriginPattern(aOriginNoSuffix)
+{
+  MOZ_ASSERT(mType == opClearMatchingOriginAttributes);
+  MOZ_COUNT_CTOR(DOMStorageDBThread::DBOperation);
+}
+
+DOMStorageDBThread::DBOperation::~DBOperation()
+{
+  MOZ_COUNT_DTOR(DOMStorageDBThread::DBOperation);
+}
+
+const nsCString
+DOMStorageDBThread::DBOperation::OriginNoSuffix() const
+{
+  if (mCache) {
+    return mCache->OriginNoSuffix();
+  }
+
+  return EmptyCString();
+}
+
+const nsCString
+DOMStorageDBThread::DBOperation::OriginSuffix() const
+{
+  if (mCache) {
+    return mCache->OriginSuffix();
+  }
+
+  return EmptyCString();
+}
+
+const nsCString
+DOMStorageDBThread::DBOperation::Origin() const
+{
+  if (mCache) {
+    return mCache->Origin();
+  }
+
+  return mOrigin;
+}
+
+const nsCString
+DOMStorageDBThread::DBOperation::Target() const
+{
+  switch (mType) {
+    case opAddItem:
+    case opUpdateItem:
+    case opRemoveItem:
+      return Origin() + NS_LITERAL_CSTRING("|") + NS_ConvertUTF16toUTF8(mKey);
+
+    default:
+      return Origin();
+  }
+}
+
+void
+DOMStorageDBThread::DBOperation::PerformAndFinalize(DOMStorageDBThread* aThread)
+{
+  Finalize(Perform(aThread));
+}
+
+nsresult
+DOMStorageDBThread::DBOperation::Perform(DOMStorageDBThread* aThread)
+{
+  nsresult rv;
+
+  switch (mType) {
+  case opPreload:
+  case opPreloadUrgent:
+  {
+    // Already loaded?
+    if (mCache->Loaded()) {
+      break;
+    }
+
+    StatementCache* statements;
+    if (MOZ_UNLIKELY(NS_IsMainThread())) {
+      statements = &aThread->mReaderStatements;
+    } else {
+      statements = &aThread->mWorkerStatements;
+    }
+
+    // OFFSET is an optimization when we have to do a sync load
+    // and cache has already loaded some parts asynchronously.
+    // It skips keys we have already loaded.
+    nsCOMPtr<mozIStorageStatement> stmt = statements->GetCachedStatement(
+        "SELECT key, value FROM webappsstore2 "
+        "WHERE originAttributes = :originAttributes AND originKey = :originKey "
+        "ORDER BY key LIMIT -1 OFFSET :offset");
+    NS_ENSURE_STATE(stmt);
+    mozStorageStatementScoper scope(stmt);
+
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("originAttributes"),
+                                    mCache->OriginSuffix());
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("originKey"),
+                                    mCache->OriginNoSuffix());
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = stmt->BindInt32ByName(NS_LITERAL_CSTRING("offset"),
+                               static_cast<int32_t>(mCache->LoadedCount()));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    bool exists;
+    while (NS_SUCCEEDED(rv = stmt->ExecuteStep(&exists)) && exists) {
+      nsAutoString key;
+      rv = stmt->GetString(0, key);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nsAutoString value;
+      rv = stmt->GetString(1, value);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (!mCache->LoadItem(key, value)) {
+        break;
+      }
+    }
+    // The loop condition's call to ExecuteStep() may have terminated because
+    // !NS_SUCCEEDED(), we need an early return to cover that case.  This also
+    // covers success cases as well, but that's inductively safe.
+    NS_ENSURE_SUCCESS(rv, rv);
+    break;
+  }
+
+  case opGetUsage:
+  {
+    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
+      "SELECT SUM(LENGTH(key) + LENGTH(value)) FROM webappsstore2 "
+      "WHERE (originAttributes || ':' || originKey) LIKE :usageOrigin"
+    );
+    NS_ENSURE_STATE(stmt);
+
+    mozStorageStatementScoper scope(stmt);
+
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("usageOrigin"),
+                                    mUsage->OriginScope());
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    bool exists;
+    rv = stmt->ExecuteStep(&exists);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    int64_t usage = 0;
+    if (exists) {
+      rv = stmt->GetInt64(0, &usage);
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+
+    mUsage->LoadUsage(usage);
+    break;
+  }
+
+  case opAddItem:
+  case opUpdateItem:
+  {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
+      "INSERT OR REPLACE INTO webappsstore2 (originAttributes, originKey, scope, key, value) "
+      "VALUES (:originAttributes, :originKey, :scope, :key, :value) "
+    );
+    NS_ENSURE_STATE(stmt);
+
+    mozStorageStatementScoper scope(stmt);
+
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("originAttributes"),
+                                    mCache->OriginSuffix());
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("originKey"),
+                                    mCache->OriginNoSuffix());
+    NS_ENSURE_SUCCESS(rv, rv);
+    // Filling the 'scope' column just for downgrade compatibility reasons
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("scope"),
+                                    Scheme0Scope(mCache));
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = stmt->BindStringByName(NS_LITERAL_CSTRING("key"),
+                                mKey);
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = stmt->BindStringByName(NS_LITERAL_CSTRING("value"),
+                                mValue);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = stmt->Execute();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MonitorAutoLock monitor(aThread->mThreadObserver->GetMonitor());
+    aThread->mOriginsHavingData.PutEntry(Origin());
+    break;
+  }
+
+  case opRemoveItem:
+  {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
+      "DELETE FROM webappsstore2 "
+      "WHERE originAttributes = :originAttributes AND originKey = :originKey "
+        "AND key = :key "
+    );
+    NS_ENSURE_STATE(stmt);
+    mozStorageStatementScoper scope(stmt);
+
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("originAttributes"),
+                                    mCache->OriginSuffix());
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("originKey"),
+                                    mCache->OriginNoSuffix());
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = stmt->BindStringByName(NS_LITERAL_CSTRING("key"),
+                                mKey);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = stmt->Execute();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    break;
+  }
+
+  case opClear:
+  {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
+      "DELETE FROM webappsstore2 "
+      "WHERE originAttributes = :originAttributes AND originKey = :originKey"
+    );
+    NS_ENSURE_STATE(stmt);
+    mozStorageStatementScoper scope(stmt);
+
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("originAttributes"),
+                                    mCache->OriginSuffix());
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("originKey"),
+                                    mCache->OriginNoSuffix());
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = stmt->Execute();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MonitorAutoLock monitor(aThread->mThreadObserver->GetMonitor());
+    aThread->mOriginsHavingData.RemoveEntry(Origin());
+    break;
+  }
+
+  case opClearAll:
+  {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
+      "DELETE FROM webappsstore2"
+    );
+    NS_ENSURE_STATE(stmt);
+    mozStorageStatementScoper scope(stmt);
+
+    rv = stmt->Execute();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MonitorAutoLock monitor(aThread->mThreadObserver->GetMonitor());
+    aThread->mOriginsHavingData.Clear();
+    break;
+  }
+
+  case opClearMatchingOrigin:
+  {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
+      "DELETE FROM webappsstore2"
+      " WHERE originKey GLOB :scope"
+    );
+    NS_ENSURE_STATE(stmt);
+    mozStorageStatementScoper scope(stmt);
+
+    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("scope"),
+                                    mOrigin + NS_LITERAL_CSTRING("*"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = stmt->Execute();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // No need to selectively clear mOriginsHavingData here.  That hashtable only
+    // prevents preload for scopes with no data.  Leaving a false record in it has
+    // a negligible effect on performance.
+    break;
+  }
+
+  case opClearMatchingOriginAttributes:
+  {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    // Register the ORIGIN_ATTRS_PATTERN_MATCH function, initialized with the pattern
+    nsCOMPtr<mozIStorageFunction> patternMatchFunction(
+      new OriginAttrsPatternMatchSQLFunction(mOriginPattern));
+
+    rv = aThread->mWorkerConnection->CreateFunction(
+      NS_LITERAL_CSTRING("ORIGIN_ATTRS_PATTERN_MATCH"), 1, patternMatchFunction);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
+      "DELETE FROM webappsstore2"
+      " WHERE ORIGIN_ATTRS_PATTERN_MATCH(originAttributes)"
+    );
+
+    if (stmt) {
+      mozStorageStatementScoper scope(stmt);
+      rv = stmt->Execute();
+    } else {
+      rv = NS_ERROR_UNEXPECTED;
+    }
+
+    // Always remove the function
+    aThread->mWorkerConnection->RemoveFunction(
+      NS_LITERAL_CSTRING("ORIGIN_ATTRS_PATTERN_MATCH"));
+
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // No need to selectively clear mOriginsHavingData here.  That hashtable only
+    // prevents preload for scopes with no data.  Leaving a false record in it has
+    // a negligible effect on performance.
+    break;
+  }
+
+  default:
+    NS_ERROR("Unknown task type");
+    break;
+  }
+
+  return NS_OK;
+}
+
+void
+DOMStorageDBThread::DBOperation::Finalize(nsresult aRv)
+{
+  switch (mType) {
+  case opPreloadUrgent:
+  case opPreload:
+    if (NS_FAILED(aRv)) {
+      // When we are here, something failed when loading from the database.
+      // Notify that the storage is loaded to prevent deadlock of the main thread,
+      // even though it is actually empty or incomplete.
+      NS_WARNING("Failed to preload localStorage");
+    }
+
+    mCache->LoadDone(aRv);
+    break;
+
+  case opGetUsage:
+    if (NS_FAILED(aRv)) {
+      mUsage->LoadUsage(0);
+    }
+
+    break;
+
+  default:
+    if (NS_FAILED(aRv)) {
+      NS_WARNING("localStorage update/clear operation failed,"
+                 " data may not persist or clean up");
+    }
+
+    break;
+  }
+}
+
+// DOMStorageDBThread::PendingOperations
+
+DOMStorageDBThread::PendingOperations::PendingOperations()
+: mFlushFailureCount(0)
+{
+}
+
+bool
+DOMStorageDBThread::PendingOperations::HasTasks() const
+{
+  return !!mUpdates.Count() || !!mClears.Count();
+}
+
+namespace {
+
+bool OriginPatternMatches(const nsACString& aOriginSuffix, const OriginAttributesPattern& aPattern)
+{
+  PrincipalOriginAttributes oa;
+  DebugOnly<bool> rv = oa.PopulateFromSuffix(aOriginSuffix);
+  MOZ_ASSERT(rv);
+  return aPattern.Matches(oa);
+}
+
+} // namespace
+
+bool
+DOMStorageDBThread::PendingOperations::CheckForCoalesceOpportunity(DBOperation* aNewOp,
+                                                                   DBOperation::OperationType aPendingType,
+                                                                   DBOperation::OperationType aNewType)
+{
+  if (aNewOp->Type() != aNewType) {
+    return false;
+  }
+
+  DOMStorageDBThread::DBOperation* pendingTask;
+  if (!mUpdates.Get(aNewOp->Target(), &pendingTask)) {
+    return false;
+  }
+
+  if (pendingTask->Type() != aPendingType) {
+    return false;
+  }
+
+  return true;
+}
+
+void
+DOMStorageDBThread::PendingOperations::Add(DOMStorageDBThread::DBOperation* aOperation)
+{
+  // Optimize: when a key to remove has never been written to disk
+  // just bypass this operation.  A key is new when an operation scheduled
+  // to write it to the database is of type opAddItem.
+  if (CheckForCoalesceOpportunity(aOperation, DBOperation::opAddItem, DBOperation::opRemoveItem)) {
+    mUpdates.Remove(aOperation->Target());
+    delete aOperation;
+    return;
+  }
+
+  // Optimize: when changing a key that is new and has never been
+  // written to disk, keep type of the operation to store it at opAddItem.
+  // This allows optimization to just forget adding a new key when
+  // it is removed from the storage before flush.
+  if (CheckForCoalesceOpportunity(aOperation, DBOperation::opAddItem, DBOperation::opUpdateItem)) {
+    aOperation->mType = DBOperation::opAddItem;
+  }
+
+  // Optimize: to prevent lose of remove operation on a key when doing
+  // remove/set/remove on a previously existing key we have to change
+  // opAddItem to opUpdateItem on the new operation when there is opRemoveItem
+  // pending for the key.
+  if (CheckForCoalesceOpportunity(aOperation, DBOperation::opRemoveItem, DBOperation::opAddItem)) {
+    aOperation->mType = DBOperation::opUpdateItem;
+  }
+
+  switch (aOperation->Type())
+  {
+  // Operations on single keys
+
+  case DBOperation::opAddItem:
+  case DBOperation::opUpdateItem:
+  case DBOperation::opRemoveItem:
+    // Override any existing operation for the target (=scope+key).
+    mUpdates.Put(aOperation->Target(), aOperation);
+    break;
+
+  // Clear operations
+
+  case DBOperation::opClear:
+  case DBOperation::opClearMatchingOrigin:
+  case DBOperation::opClearMatchingOriginAttributes:
+    // Drop all update (insert/remove) operations for equivavelent or matching scope.
+    // We do this as an optimization as well as a must based on the logic,
+    // if we would not delete the update tasks, changes would have been stored
+    // to the database after clear operations have been executed.
+    for (auto iter = mUpdates.Iter(); !iter.Done(); iter.Next()) {
+      nsAutoPtr<DBOperation>& pendingTask = iter.Data();
+
+      if (aOperation->Type() == DBOperation::opClear &&
+          (pendingTask->OriginNoSuffix() != aOperation->OriginNoSuffix() ||
+           pendingTask->OriginSuffix() != aOperation->OriginSuffix())) {
+        continue;
+      }
+
+      if (aOperation->Type() == DBOperation::opClearMatchingOrigin &&
+          !StringBeginsWith(pendingTask->OriginNoSuffix(), aOperation->Origin())) {
+        continue;
+      }
+
+      if (aOperation->Type() == DBOperation::opClearMatchingOriginAttributes &&
+          !OriginPatternMatches(pendingTask->OriginSuffix(), aOperation->OriginPattern())) {
+        continue;
+      }
+
+      iter.Remove();
+    }
+
+    mClears.Put(aOperation->Target(), aOperation);
+    break;
+
+  case DBOperation::opClearAll:
+    // Drop simply everything, this is a super-operation.
+    mUpdates.Clear();
+    mClears.Clear();
+    mClears.Put(aOperation->Target(), aOperation);
+    break;
+
+  default:
+    MOZ_ASSERT(false);
+    break;
+  }
+}
+
+bool
+DOMStorageDBThread::PendingOperations::Prepare()
+{
+  // Called under the lock
+
+  // First collect clear operations and then updates, we can
+  // do this since whenever a clear operation for a scope is
+  // scheduled, we drop all updates matching that scope. So,
+  // all scope-related update operations we have here now were
+  // scheduled after the clear operations.
+  for (auto iter = mClears.Iter(); !iter.Done(); iter.Next()) {
+    mExecList.AppendElement(iter.Data().forget());
+  }
+  mClears.Clear();
+
+  for (auto iter = mUpdates.Iter(); !iter.Done(); iter.Next()) {
+    mExecList.AppendElement(iter.Data().forget());
+  }
+  mUpdates.Clear();
+
+  return !!mExecList.Length();
+}
+
+nsresult
+DOMStorageDBThread::PendingOperations::Execute(DOMStorageDBThread* aThread)
+{
+  // Called outside the lock
+
+  mozStorageTransaction transaction(aThread->mWorkerConnection, false);
+
+  nsresult rv;
+
+  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
+    DOMStorageDBThread::DBOperation* task = mExecList[i];
+    rv = task->Perform(aThread);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  rv = transaction.Commit();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+bool
+DOMStorageDBThread::PendingOperations::Finalize(nsresult aRv)
+{
+  // Called under the lock
+
+  // The list is kept on a failure to retry it
+  if (NS_FAILED(aRv)) {
+    // XXX Followup: we may try to reopen the database and flush these
+    // pending tasks, however testing showed that even though I/O is actually
+    // broken some amount of operations is left in sqlite+system buffers and
+    // seems like successfully flushed to disk.
+    // Tested by removing a flash card and disconnecting from network while
+    // using a network drive on Windows system.
+    NS_WARNING("Flush operation on localStorage database failed");
+
+    ++mFlushFailureCount;
+
+    return mFlushFailureCount >= 5;
+  }
+
+  mFlushFailureCount = 0;
+  mExecList.Clear();
+  return true;
+}
+
+namespace {
+
+bool
+FindPendingClearForOrigin(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+                         DOMStorageDBThread::DBOperation* aPendingOperation)
+{
+  if (aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opClearAll) {
+    return true;
+  }
+
+  if (aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opClear &&
+      aOriginNoSuffix == aPendingOperation->OriginNoSuffix() &&
+      aOriginSuffix == aPendingOperation->OriginSuffix()) {
+    return true;
+  }
+
+  if (aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opClearMatchingOrigin &&
+      StringBeginsWith(aOriginNoSuffix, aPendingOperation->Origin())) {
+    return true;
+  }
+
+  if (aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opClearMatchingOriginAttributes &&
+      OriginPatternMatches(aOriginSuffix, aPendingOperation->OriginPattern())) {
+    return true;
+  }
+
+  return false;
+}
+
+} // namespace
+
+bool
+DOMStorageDBThread::PendingOperations::IsOriginClearPending(const nsACString& aOriginSuffix,
+                                                            const nsACString& aOriginNoSuffix) const
+{
+  // Called under the lock
+
+  for (auto iter = mClears.ConstIter(); !iter.Done(); iter.Next()) {
+    if (FindPendingClearForOrigin(aOriginSuffix, aOriginNoSuffix, iter.UserData())) {
+      return true;
+    }
+  }
+
+  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
+    if (FindPendingClearForOrigin(aOriginSuffix, aOriginNoSuffix, mExecList[i])) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+namespace {
+
+bool
+FindPendingUpdateForOrigin(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+                           DOMStorageDBThread::DBOperation* aPendingOperation)
+{
+  if ((aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opAddItem ||
+       aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opUpdateItem ||
+       aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opRemoveItem) &&
+       aOriginNoSuffix == aPendingOperation->OriginNoSuffix() &&
+       aOriginSuffix == aPendingOperation->OriginSuffix()) {
+    return true;
+  }
+
+  return false;
+}
+
+} // namespace
+
+bool
+DOMStorageDBThread::PendingOperations::IsOriginUpdatePending(const nsACString& aOriginSuffix,
+                                                             const nsACString& aOriginNoSuffix) const
+{
+  // Called under the lock
+
+  for (auto iter = mUpdates.ConstIter(); !iter.Done(); iter.Next()) {
+    if (FindPendingUpdateForOrigin(aOriginSuffix, aOriginNoSuffix, iter.UserData())) {
+      return true;
+    }
+  }
+
+  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
+    if (FindPendingUpdateForOrigin(aOriginSuffix, aOriginNoSuffix, mExecList[i])) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/DOMStorageDBThread.h b/dom/storage/DOMStorageDBThread.h
new file mode 100644
index 0000000000..0efaebaa31
--- /dev/null
+++ b/dom/storage/DOMStorageDBThread.h
@@ -0,0 +1,407 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 DOMStorageDBThread_h___
+#define DOMStorageDBThread_h___
+
+#include "prthread.h"
+#include "prinrval.h"
+#include "nsTArray.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/storage/StatementCache.h"
+#include "nsAutoPtr.h"
+#include "nsString.h"
+#include "nsCOMPtr.h"
+#include "nsClassHashtable.h"
+#include "nsIFile.h"
+#include "nsIThreadInternal.h"
+
+class mozIStorageConnection;
+
+namespace mozilla {
+namespace dom {
+
+class DOMStorageCacheBridge;
+class DOMStorageUsageBridge;
+class DOMStorageUsage;
+
+typedef mozilla::storage::StatementCache<mozIStorageStatement> StatementCache;
+
+// Interface used by the cache to post operations to the asynchronous
+// database thread or process.
+class DOMStorageDBBridge
+{
+public:
+  DOMStorageDBBridge();
+  virtual ~DOMStorageDBBridge() {}
+
+  // Ensures the database engine is started
+  virtual nsresult Init() = 0;
+
+  // Releases the database and disallows its usage
+  virtual nsresult Shutdown() = 0;
+
+  // Asynchronously fills the cache with data from the database for first use.
+  // When |aPriority| is true, the preload operation is scheduled as the first one.
+  // This method is responsible to keep hard reference to the cache for the time of
+  // the preload or, when preload cannot be performed, call LoadDone() immediately.
+  virtual void AsyncPreload(DOMStorageCacheBridge* aCache, bool aPriority = false) = 0;
+
+  // Asynchronously fill the |usage| object with actual usage of data by its scope.
+  // The scope is eTLD+1 tops, never deeper subdomains.
+  virtual void AsyncGetUsage(DOMStorageUsageBridge* aUsage) = 0;
+
+  // Synchronously fills the cache, when |aForceSync| is false and cache already got some
+  // data before, the method waits for the running preload to finish
+  virtual void SyncPreload(DOMStorageCacheBridge* aCache, bool aForceSync = false) = 0;
+
+  // Called when an existing key is modified in the storage, schedules update to the database
+  virtual nsresult AsyncAddItem(DOMStorageCacheBridge* aCache, const nsAString& aKey, const nsAString& aValue) = 0;
+
+  // Called when an existing key is modified in the storage, schedules update to the database
+  virtual nsresult AsyncUpdateItem(DOMStorageCacheBridge* aCache, const nsAString& aKey, const nsAString& aValue) = 0;
+
+  // Called when an item is removed from the storage, schedules delete of the key
+  virtual nsresult AsyncRemoveItem(DOMStorageCacheBridge* aCache, const nsAString& aKey) = 0;
+
+  // Called when the whole storage is cleared by the DOM API, schedules delete of the scope
+  virtual nsresult AsyncClear(DOMStorageCacheBridge* aCache) = 0;
+
+  // Called when chrome deletes e.g. cookies, schedules delete of the whole database
+  virtual void AsyncClearAll() = 0;
+
+  // Called when only a domain and its subdomains is about to clear
+  virtual void AsyncClearMatchingOrigin(const nsACString& aOriginNoSuffix) = 0;
+
+  // Called when data matching an origin pattern have to be cleared
+  virtual void AsyncClearMatchingOriginAttributes(const OriginAttributesPattern& aPattern) = 0;
+
+  // Forces scheduled DB operations to be early flushed to the disk
+  virtual void AsyncFlush() = 0;
+
+  // Check whether the scope has any data stored on disk and is thus allowed to preload
+  virtual bool ShouldPreloadOrigin(const nsACString& aOriginNoSuffix) = 0;
+
+  // Get the complete list of scopes having data
+  virtual void GetOriginsHavingData(InfallibleTArray<nsCString>* aOrigins) = 0;
+};
+
+// The implementation of the the database engine, this directly works
+// with the sqlite or any other db API we are based on
+// This class is resposible for collecting and processing asynchronous 
+// DB operations over caches (DOMStorageCache) communicating though 
+// DOMStorageCacheBridge interface class
+class DOMStorageDBThread final : public DOMStorageDBBridge
+{
+public:
+  class PendingOperations;
+
+  // Representation of a singe database task, like adding and removing keys,
+  // (pre)loading the whole origin data, cleaning.
+  class DBOperation
+  {
+  public:
+    typedef enum {
+      // Only operation that reads data from the database
+      opPreload,
+      // The same as opPreload, just executed with highest priority
+      opPreloadUrgent,
+
+      // Load usage of a scope
+      opGetUsage,
+
+      // Operations invoked by the DOM content API
+      opAddItem,
+      opUpdateItem,
+      opRemoveItem,
+      // Clears a specific single origin data
+      opClear,
+
+      // Operations invoked by chrome
+
+      // Clear all the data stored in the database, for all scopes, no exceptions
+      opClearAll,
+      // Clear data under a domain and all its subdomains regardless OriginAttributes value
+      opClearMatchingOrigin,
+      // Clear all data matching an OriginAttributesPattern regardless a domain
+      opClearMatchingOriginAttributes,
+    } OperationType;
+
+    explicit DBOperation(const OperationType aType,
+                         DOMStorageCacheBridge* aCache = nullptr,
+                         const nsAString& aKey = EmptyString(),
+                         const nsAString& aValue = EmptyString());
+    DBOperation(const OperationType aType,
+                DOMStorageUsageBridge* aUsage);
+    DBOperation(const OperationType aType,
+                const nsACString& aOriginNoSuffix);
+    DBOperation(const OperationType aType,
+                const OriginAttributesPattern& aOriginNoSuffix);
+    ~DBOperation();
+
+    // Executes the operation, doesn't necessarity have to be called on the I/O thread
+    void PerformAndFinalize(DOMStorageDBThread* aThread);
+
+    // Finalize the operation, i.e. do any internal cleanup and finish calls
+    void Finalize(nsresult aRv);
+
+    // The operation type
+    OperationType Type() const { return mType; }
+
+    // The origin in the database usage format (reversed)
+    const nsCString OriginNoSuffix() const;
+
+    // The origin attributes suffix
+    const nsCString OriginSuffix() const;
+
+    // |origin suffix + origin key| the operation is working with
+    // or a scope pattern to delete with simple SQL's "LIKE %" from the database.
+    const nsCString Origin() const;
+
+    // |origin suffix + origin key + key| the operation is working with
+    const nsCString Target() const;
+
+    // Pattern to delete matching data with this op
+    const OriginAttributesPattern& OriginPattern() const { return mOriginPattern; }
+
+  private:
+    // The operation implementation body
+    nsresult Perform(DOMStorageDBThread* aThread);
+
+    friend class PendingOperations;
+    OperationType mType;
+    RefPtr<DOMStorageCacheBridge> mCache;
+    RefPtr<DOMStorageUsageBridge> mUsage;
+    nsString const mKey;
+    nsString const mValue;
+    nsCString const mOrigin;
+    OriginAttributesPattern const mOriginPattern;
+  };
+
+  // Encapsulation of collective and coalescing logic for all pending operations
+  // except preloads that are handled separately as priority operations
+  class PendingOperations {
+  public:
+    PendingOperations();
+
+    // Method responsible for coalescing redundant update operations with the same
+    // |Target()| or clear operations with the same or matching |Origin()|
+    void Add(DBOperation* aOperation);
+
+    // True when there are some scheduled operations to flush on disk
+    bool HasTasks() const;
+
+    // Moves collected operations to a local flat list to allow execution of the operation
+    // list out of the thread lock
+    bool Prepare();
+
+    // Executes the previously |Prepared()'ed| list of operations, retuns result, but doesn't
+    // handle it in any way in case of a failure
+    nsresult Execute(DOMStorageDBThread* aThread);
+
+    // Finalizes the pending operation list, returns false when too many operations failed
+    // to flush what indicates a long standing issue with the database access.
+    bool Finalize(nsresult aRv);
+
+    // true when a clear that deletes the given origin attr pattern and/or origin key
+    // is among the pending operations; when a preload for that scope is being scheduled,
+    // it must be finished right away
+    bool IsOriginClearPending(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix) const;
+
+    // Checks whether there is a pending update operation for this scope.
+    bool IsOriginUpdatePending(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix) const;
+
+  private:
+    // Returns true iff new operation is of type newType and there is a pending 
+    // operation of type pendingType for the same key (target).
+    bool CheckForCoalesceOpportunity(DBOperation* aNewOp,
+                                     DBOperation::OperationType aPendingType,
+                                     DBOperation::OperationType aNewType);
+
+    // List of all clearing operations, executed first
+    nsClassHashtable<nsCStringHashKey, DBOperation> mClears;
+
+    // List of all update/insert operations, executed as second
+    nsClassHashtable<nsCStringHashKey, DBOperation> mUpdates;
+
+    // Collection of all tasks, valid only between Prepare() and Execute()
+    nsTArray<nsAutoPtr<DBOperation> > mExecList;
+
+    // Number of failing flush attempts
+    uint32_t mFlushFailureCount;
+  };
+
+  class ThreadObserver final : public nsIThreadObserver
+  {
+    NS_DECL_THREADSAFE_ISUPPORTS
+    NS_DECL_NSITHREADOBSERVER
+
+    ThreadObserver()
+      : mHasPendingEvents(false)
+      , mMonitor("DOMStorageThreadMonitor")
+    {
+    }
+
+    bool HasPendingEvents() {
+      mMonitor.AssertCurrentThreadOwns();
+      return mHasPendingEvents;
+    }
+    void ClearPendingEvents() {
+      mMonitor.AssertCurrentThreadOwns();
+      mHasPendingEvents = false;
+    }
+    Monitor& GetMonitor() { return mMonitor; }
+
+  private:
+    virtual ~ThreadObserver() {}
+    bool mHasPendingEvents;
+    // The monitor we drive the thread with
+    Monitor mMonitor;
+  };
+
+public:
+  DOMStorageDBThread();
+  virtual ~DOMStorageDBThread() {}
+
+  virtual nsresult Init();
+  virtual nsresult Shutdown();
+
+  virtual void AsyncPreload(DOMStorageCacheBridge* aCache, bool aPriority = false)
+    { InsertDBOp(new DBOperation(aPriority ? DBOperation::opPreloadUrgent : DBOperation::opPreload, aCache)); }
+
+  virtual void SyncPreload(DOMStorageCacheBridge* aCache, bool aForce = false);
+
+  virtual void AsyncGetUsage(DOMStorageUsageBridge * aUsage)
+    { InsertDBOp(new DBOperation(DBOperation::opGetUsage, aUsage)); }
+
+  virtual nsresult AsyncAddItem(DOMStorageCacheBridge* aCache, const nsAString& aKey, const nsAString& aValue)
+    { return InsertDBOp(new DBOperation(DBOperation::opAddItem, aCache, aKey, aValue)); }
+
+  virtual nsresult AsyncUpdateItem(DOMStorageCacheBridge* aCache, const nsAString& aKey, const nsAString& aValue)
+    { return InsertDBOp(new DBOperation(DBOperation::opUpdateItem, aCache, aKey, aValue)); }
+
+  virtual nsresult AsyncRemoveItem(DOMStorageCacheBridge* aCache, const nsAString& aKey)
+    { return InsertDBOp(new DBOperation(DBOperation::opRemoveItem, aCache, aKey)); }
+
+  virtual nsresult AsyncClear(DOMStorageCacheBridge* aCache)
+    { return InsertDBOp(new DBOperation(DBOperation::opClear, aCache)); }
+
+  virtual void AsyncClearAll()
+    { InsertDBOp(new DBOperation(DBOperation::opClearAll)); }
+
+  virtual void AsyncClearMatchingOrigin(const nsACString& aOriginNoSuffix)
+    { InsertDBOp(new DBOperation(DBOperation::opClearMatchingOrigin, aOriginNoSuffix)); }
+
+  virtual void AsyncClearMatchingOriginAttributes(const OriginAttributesPattern& aPattern)
+    { InsertDBOp(new DBOperation(DBOperation::opClearMatchingOriginAttributes, aPattern)); }
+
+  virtual void AsyncFlush();
+
+  virtual bool ShouldPreloadOrigin(const nsACString& aOrigin);
+  virtual void GetOriginsHavingData(InfallibleTArray<nsCString>* aOrigins);
+
+private:
+  nsCOMPtr<nsIFile> mDatabaseFile;
+  PRThread* mThread;
+
+  // Used to observe runnables dispatched to our thread and to monitor it.
+  RefPtr<ThreadObserver> mThreadObserver;
+
+  // Flag to stop, protected by the monitor returned by
+  // mThreadObserver->GetMonitor().
+  bool mStopIOThread;
+
+  // Whether WAL is enabled
+  bool mWALModeEnabled;
+
+  // Whether DB has already been open, avoid races between main thread reads
+  // and pending DB init in the background I/O thread
+  Atomic<bool, ReleaseAcquire> mDBReady;
+
+  // State of the database initiation
+  nsresult mStatus;
+
+  // List of origins (including origin attributes suffix) having data, for optimization purposes only
+  nsTHashtable<nsCStringHashKey> mOriginsHavingData;
+
+  // Connection used by the worker thread for all read and write ops
+  nsCOMPtr<mozIStorageConnection> mWorkerConnection;
+
+  // Connection used only on the main thread for sync read operations
+  nsCOMPtr<mozIStorageConnection> mReaderConnection;
+
+  StatementCache mWorkerStatements;
+  StatementCache mReaderStatements;
+
+  // Time the first pending operation has been added to the pending operations
+  // list
+  PRIntervalTime mDirtyEpoch;
+
+  // Flag to force immediate flush of all pending operations
+  bool mFlushImmediately;
+
+  // List of preloading operations, in chronological or priority order.
+  // Executed prioritly over pending update operations.
+  nsTArray<DBOperation*> mPreloads;
+
+  // Collector of pending update operations
+  PendingOperations mPendingTasks;
+
+  // Counter of calls for thread priority rising.
+  int32_t mPriorityCounter;
+
+  // Helper to direct an operation to one of the arrays above;
+  // also checks IsOriginClearPending for preloads
+  nsresult InsertDBOp(DBOperation* aOperation);
+
+  // Opens the database, first thing we do after start of the thread.
+  nsresult OpenDatabaseConnection();
+  nsresult OpenAndUpdateDatabase();
+  nsresult InitDatabase();
+  nsresult ShutdownDatabase();
+
+  // Tries to establish WAL mode
+  nsresult SetJournalMode(bool aIsWal);
+  nsresult TryJournalMode();
+
+  // Sets the threshold for auto-checkpointing the WAL.
+  nsresult ConfigureWALBehavior();
+
+  void SetHigherPriority();
+  void SetDefaultPriority();
+
+  // Ensures we flush pending tasks in some reasonble time
+  void ScheduleFlush();
+
+  // Called when flush of pending tasks is being executed
+  void UnscheduleFlush();
+
+  // This method is used for two purposes:
+  // 1. as a value passed to monitor.Wait() method
+  // 2. as in indicator that flush has to be performed
+  //
+  // Return:
+  // - PR_INTERVAL_NO_TIMEOUT when no pending tasks are scheduled
+  // - larger then zero when tasks have been scheduled, but it is
+  //   still not time to perform the flush ; it is actual interval
+  //   time to wait until the flush has to happen
+  // - 0 when it is time to do the flush
+  PRIntervalTime TimeUntilFlush();
+
+  // Notifies to the main thread that flush has completed
+  void NotifyFlushCompletion();
+
+  // Thread loop
+  static void ThreadFunc(void* aArg);
+  void ThreadFunc();
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif /* DOMStorageDBThread_h___ */
diff --git a/dom/storage/DOMStorageDBUpdater.cpp b/dom/storage/DOMStorageDBUpdater.cpp
new file mode 100644
index 0000000000..8e3f07d7ce
--- /dev/null
+++ b/dom/storage/DOMStorageDBUpdater.cpp
@@ -0,0 +1,417 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "DOMStorageManager.h"
+
+#include "mozIStorageBindingParamsArray.h"
+#include "mozIStorageBindingParams.h"
+#include "mozIStorageValueArray.h"
+#include "mozIStorageFunction.h"
+#include "mozilla/BasePrincipal.h"
+#include "nsVariant.h"
+#include "mozilla/Services.h"
+#include "mozilla/Tokenizer.h"
+
+// Current version of the database schema
+#define CURRENT_SCHEMA_VERSION 1
+
+namespace mozilla {
+namespace dom {
+
+extern void
+ReverseString(const nsCSubstring& aSource, nsCSubstring& aResult);
+
+namespace {
+
+class nsReverseStringSQLFunction final : public mozIStorageFunction
+{
+  ~nsReverseStringSQLFunction() {}
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_MOZISTORAGEFUNCTION
+};
+
+NS_IMPL_ISUPPORTS(nsReverseStringSQLFunction, mozIStorageFunction)
+
+NS_IMETHODIMP
+nsReverseStringSQLFunction::OnFunctionCall(
+    mozIStorageValueArray* aFunctionArguments, nsIVariant** aResult)
+{
+  nsresult rv;
+
+  nsAutoCString stringToReverse;
+  rv = aFunctionArguments->GetUTF8String(0, stringToReverse);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsAutoCString result;
+  ReverseString(stringToReverse, result);
+
+  RefPtr<nsVariant> outVar(new nsVariant());
+  rv = outVar->SetAsAUTF8String(result);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  outVar.forget(aResult);
+  return NS_OK;
+}
+
+// "scope" to "origin attributes suffix" and "origin key" convertor
+
+class ExtractOriginData : protected mozilla::Tokenizer
+{
+public:
+  ExtractOriginData(const nsACString& scope, nsACString& suffix, nsACString& origin)
+    : mozilla::Tokenizer(scope)
+  {
+    using mozilla::OriginAttributes;
+
+    // Parse optional appId:isInIsolatedMozBrowserElement: string, in case
+    // we don't find it, the scope is our new origin key and suffix
+    // is empty.
+    suffix.Truncate();
+    origin.Assign(scope);
+
+    // Bail out if it isn't appId.
+    uint32_t appId;
+    if (!ReadInteger(&appId)) {
+      return;
+    }
+
+    // Should be followed by a colon.
+    if (!CheckChar(':')) {
+      return;
+    }
+
+    // Bail out if it isn't 'isolatedBrowserFlag'.
+    nsDependentCSubstring isolatedBrowserFlag;
+    if (!ReadWord(isolatedBrowserFlag)) {
+      return;
+    }
+
+    bool inIsolatedMozBrowser = isolatedBrowserFlag == "t";
+    bool notInIsolatedBrowser = isolatedBrowserFlag == "f";
+    if (!inIsolatedMozBrowser && !notInIsolatedBrowser) {
+      return;
+    }
+
+    // Should be followed by a colon.
+    if (!CheckChar(':')) {
+      return;
+    }
+
+    // OK, we have found appId and inIsolatedMozBrowser flag, create the suffix
+    // from it and take the rest as the origin key.
+
+    // If the profile went through schema 1 -> schema 0 -> schema 1 switching
+    // we may have stored the full attributes origin suffix when there were
+    // more than just appId and inIsolatedMozBrowser set on storage principal's
+    // OriginAttributes.
+    //
+    // To preserve full uniqueness we store this suffix to the scope key.
+    // Schema 0 code will just ignore it while keeping the scoping unique.
+    //
+    // The whole scope string is in one of the following forms (when we are here):
+    //
+    // "1001:f:^appId=1001&inBrowser=false&addonId=101:gro.allizom.rxd.:https:443"
+    // "1001:f:gro.allizom.rxd.:https:443"
+    //         |
+    //         +- the parser cursor position.
+    //
+    // If there is '^', the full origin attributes suffix follows.  We search
+    // for ':' since it is the delimiter used in the scope string and is never
+    // contained in the origin attributes suffix.  Remaining string after
+    // the comma is the reversed-domain+schema+port tuple.
+    Record();
+    if (CheckChar('^')) {
+      Token t;
+      while (Next(t)) {
+        if (t.Equals(Token::Char(':'))) {
+          Claim(suffix);
+          break;
+        }
+      }
+    } else {
+      PrincipalOriginAttributes attrs(appId, inIsolatedMozBrowser);
+      attrs.CreateSuffix(suffix);
+    }
+
+    // Consume the rest of the input as "origin".
+    origin.Assign(Substring(mCursor, mEnd));
+  }
+};
+
+class GetOriginParticular final : public mozIStorageFunction
+{
+public:
+  enum EParticular {
+    ORIGIN_ATTRIBUTES_SUFFIX,
+    ORIGIN_KEY
+  };
+
+  explicit GetOriginParticular(EParticular aParticular)
+    : mParticular(aParticular) {}
+
+private:
+  GetOriginParticular() = delete;
+  ~GetOriginParticular() {}
+
+  EParticular mParticular;
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_MOZISTORAGEFUNCTION
+};
+
+NS_IMPL_ISUPPORTS(GetOriginParticular, mozIStorageFunction)
+
+NS_IMETHODIMP
+GetOriginParticular::OnFunctionCall(
+    mozIStorageValueArray* aFunctionArguments, nsIVariant** aResult)
+{
+  nsresult rv;
+
+  nsAutoCString scope;
+  rv = aFunctionArguments->GetUTF8String(0, scope);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsAutoCString suffix, origin;
+  ExtractOriginData(scope, suffix, origin);
+
+  nsCOMPtr<nsIWritableVariant> outVar(new nsVariant());
+
+  switch (mParticular) {
+  case EParticular::ORIGIN_ATTRIBUTES_SUFFIX:
+    rv = outVar->SetAsAUTF8String(suffix);
+    break;
+  case EParticular::ORIGIN_KEY:
+    rv = outVar->SetAsAUTF8String(origin);
+    break;
+  }
+
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  outVar.forget(aResult);
+  return NS_OK;
+}
+
+} // namespace
+
+namespace DOMStorageDBUpdater {
+
+nsresult CreateSchema1Tables(mozIStorageConnection *aWorkerConnection)
+{
+  nsresult rv;
+
+  rv = aWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
+          "CREATE TABLE IF NOT EXISTS webappsstore2 ("
+          "originAttributes TEXT, "
+          "originKey TEXT, "
+          "scope TEXT, " // Only for schema0 downgrade compatibility
+          "key TEXT, "
+          "value TEXT)"));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = aWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
+        "CREATE UNIQUE INDEX IF NOT EXISTS origin_key_index"
+        " ON webappsstore2(originAttributes, originKey, key)"));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult Update(mozIStorageConnection *aWorkerConnection)
+{
+  nsresult rv;
+
+  mozStorageTransaction transaction(aWorkerConnection, false);
+
+  bool doVacuum = false;
+
+  int32_t schemaVer;
+  rv = aWorkerConnection->GetSchemaVersion(&schemaVer);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // downgrade (v0) -> upgrade (v1+) specific code
+  if (schemaVer >= 1) {
+    bool schema0IndexExists;
+    rv = aWorkerConnection->IndexExists(NS_LITERAL_CSTRING("scope_key_index"),
+                                        &schema0IndexExists);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (schema0IndexExists) {
+      // If this index exists, the database (already updated to schema >1)
+      // has been run again on schema 0 code.  That recreated that index
+      // and might store some new rows while updating only the 'scope' column.
+      // For such added rows we must fill the new 'origin*' columns correctly
+      // otherwise there would be a data loss.  The safest way to do it is to
+      // simply run the whole update to schema 1 again.
+      schemaVer = 0;
+    }
+  }
+
+  switch (schemaVer) {
+  case 0: {
+    bool webappsstore2Exists, webappsstoreExists, moz_webappsstoreExists;
+
+    rv = aWorkerConnection->TableExists(NS_LITERAL_CSTRING("webappsstore2"),
+                                        &webappsstore2Exists);
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = aWorkerConnection->TableExists(NS_LITERAL_CSTRING("webappsstore"),
+                                        &webappsstoreExists);
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = aWorkerConnection->TableExists(NS_LITERAL_CSTRING("moz_webappsstore"),
+                                        &moz_webappsstoreExists);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (!webappsstore2Exists && !webappsstoreExists && !moz_webappsstoreExists) {
+      // The database is empty, this is the first start.  Just create the schema table
+      // and break to the next version to update to, i.e. bypass update from the old version.
+
+      rv = CreateSchema1Tables(aWorkerConnection);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->SetSchemaVersion(CURRENT_SCHEMA_VERSION);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      break;
+    }
+
+    doVacuum = true;
+
+    // Ensure Gecko 1.9.1 storage table
+    rv = aWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
+           "CREATE TABLE IF NOT EXISTS webappsstore2 ("
+           "scope TEXT, "
+           "key TEXT, "
+           "value TEXT, "
+           "secure INTEGER, "
+           "owner TEXT)"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = aWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
+          "CREATE UNIQUE INDEX IF NOT EXISTS scope_key_index"
+          " ON webappsstore2(scope, key)"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<mozIStorageFunction> function1(new nsReverseStringSQLFunction());
+    NS_ENSURE_TRUE(function1, NS_ERROR_OUT_OF_MEMORY);
+
+    rv = aWorkerConnection->CreateFunction(NS_LITERAL_CSTRING("REVERSESTRING"), 1, function1);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // Check if there is storage of Gecko 1.9.0 and if so, upgrade that storage
+    // to actual webappsstore2 table and drop the obsolete table. First process
+    // this newer table upgrade to priority potential duplicates from older
+    // storage table.
+    if (webappsstoreExists) {
+      rv = aWorkerConnection->ExecuteSimpleSQL(
+        NS_LITERAL_CSTRING("INSERT OR IGNORE INTO "
+                           "webappsstore2(scope, key, value, secure, owner) "
+                           "SELECT REVERSESTRING(domain) || '.:', key, value, secure, owner "
+                           "FROM webappsstore"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->ExecuteSimpleSQL(
+        NS_LITERAL_CSTRING("DROP TABLE webappsstore"));
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+
+    // Check if there is storage of Gecko 1.8 and if so, upgrade that storage
+    // to actual webappsstore2 table and drop the obsolete table. Potential
+    // duplicates will be ignored.
+    if (moz_webappsstoreExists) {
+      rv = aWorkerConnection->ExecuteSimpleSQL(
+        NS_LITERAL_CSTRING("INSERT OR IGNORE INTO "
+                           "webappsstore2(scope, key, value, secure, owner) "
+                           "SELECT REVERSESTRING(domain) || '.:', key, value, secure, domain "
+                           "FROM moz_webappsstore"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->ExecuteSimpleSQL(
+        NS_LITERAL_CSTRING("DROP TABLE moz_webappsstore"));
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+
+    aWorkerConnection->RemoveFunction(NS_LITERAL_CSTRING("REVERSESTRING"));
+
+    // Update the scoping to match the new implememntation: split to oa suffix and origin key
+    // First rename the old table, we want to remove some columns no longer needed,
+    // but even before that drop all indexes from it (CREATE IF NOT EXISTS for index on the
+    // new table would falsely find the index!)
+    rv = aWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
+          "DROP INDEX IF EXISTS webappsstore2.origin_key_index"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = aWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
+          "DROP INDEX IF EXISTS webappsstore2.scope_key_index"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = aWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
+          "ALTER TABLE webappsstore2 RENAME TO webappsstore2_old"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<mozIStorageFunction> oaSuffixFunc(
+      new GetOriginParticular(GetOriginParticular::ORIGIN_ATTRIBUTES_SUFFIX));
+    rv = aWorkerConnection->CreateFunction(NS_LITERAL_CSTRING("GET_ORIGIN_SUFFIX"), 1, oaSuffixFunc);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<mozIStorageFunction> originKeyFunc(
+      new GetOriginParticular(GetOriginParticular::ORIGIN_KEY));
+    rv = aWorkerConnection->CreateFunction(NS_LITERAL_CSTRING("GET_ORIGIN_KEY"), 1, originKeyFunc);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // Here we ensure this schema tables when we are updating.
+    rv = CreateSchema1Tables(aWorkerConnection);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = aWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
+          "INSERT OR IGNORE INTO "
+          "webappsstore2 (originAttributes, originKey, scope, key, value) "
+          "SELECT GET_ORIGIN_SUFFIX(scope), GET_ORIGIN_KEY(scope), scope, key, value "
+          "FROM webappsstore2_old"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = aWorkerConnection->ExecuteSimpleSQL(
+      NS_LITERAL_CSTRING("DROP TABLE webappsstore2_old"));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    aWorkerConnection->RemoveFunction(NS_LITERAL_CSTRING("GET_ORIGIN_SUFFIX"));
+    aWorkerConnection->RemoveFunction(NS_LITERAL_CSTRING("GET_ORIGIN_KEY"));
+
+    rv = aWorkerConnection->SetSchemaVersion(1);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MOZ_FALLTHROUGH;
+  }
+  case CURRENT_SCHEMA_VERSION:
+    // Ensure the tables and indexes are up.  This is mostly a no-op
+    // in common scenarios.
+    rv = CreateSchema1Tables(aWorkerConnection);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // Nothing more to do here, this is the current schema version
+    break;
+
+  default:
+    MOZ_ASSERT(false);
+    break;
+  } // switch
+
+  rv = transaction.Commit();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (doVacuum) {
+    // In some cases this can make the disk file of the database significantly smaller.
+    // VACUUM cannot be executed inside a transaction.
+    rv = aWorkerConnection->ExecuteSimpleSQL(
+      NS_LITERAL_CSTRING("VACUUM"));
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return NS_OK;
+}
+
+} // namespace DOMStorageDBUpdater
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/DOMStorageDBUpdater.h b/dom/storage/DOMStorageDBUpdater.h
new file mode 100644
index 0000000000..6ab4622bce
--- /dev/null
+++ b/dom/storage/DOMStorageDBUpdater.h
@@ -0,0 +1,22 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 DOMStorageDBUpdater_h___
+#define DOMStorageDBUpdater_h___
+
+namespace mozilla {
+namespace dom {
+
+namespace DOMStorageDBUpdater {
+
+nsresult Update(mozIStorageConnection *aWorkerConnection);
+
+} // DOMStorageDBUpdater
+
+} // dom
+} // mozilla
+
+#endif
diff --git a/dom/storage/DOMStorageIPC.cpp b/dom/storage/DOMStorageIPC.cpp
new file mode 100644
index 0000000000..a8cd745f1f
--- /dev/null
+++ b/dom/storage/DOMStorageIPC.cpp
@@ -0,0 +1,770 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "DOMStorageIPC.h"
+
+#include "DOMStorageManager.h"
+
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/Unused.h"
+#include "nsIDiskSpaceWatcher.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+namespace dom {
+
+// ----------------------------------------------------------------------------
+// Child
+// ----------------------------------------------------------------------------
+
+NS_IMPL_ADDREF(DOMStorageDBChild)
+
+NS_IMETHODIMP_(MozExternalRefCountType) DOMStorageDBChild::Release(void)
+{
+  NS_PRECONDITION(0 != mRefCnt, "dup release");
+  nsrefcnt count = --mRefCnt;
+  NS_LOG_RELEASE(this, count, "DOMStorageDBChild");
+  if (count == 1 && mIPCOpen) {
+    Send__delete__(this);
+    return 0;
+  }
+  if (count == 0) {
+    mRefCnt = 1;
+    delete this;
+    return 0;
+  }
+  return count;
+}
+
+void
+DOMStorageDBChild::AddIPDLReference()
+{
+  MOZ_ASSERT(!mIPCOpen, "Attempting to retain multiple IPDL references");
+  mIPCOpen = true;
+  AddRef();
+}
+
+void
+DOMStorageDBChild::ReleaseIPDLReference()
+{
+  MOZ_ASSERT(mIPCOpen, "Attempting to release non-existent IPDL reference");
+  mIPCOpen = false;
+  Release();
+}
+
+DOMStorageDBChild::DOMStorageDBChild(DOMLocalStorageManager* aManager)
+  : mManager(aManager)
+  , mStatus(NS_OK)
+  , mIPCOpen(false)
+{
+}
+
+DOMStorageDBChild::~DOMStorageDBChild()
+{
+}
+
+nsTHashtable<nsCStringHashKey>&
+DOMStorageDBChild::OriginsHavingData()
+{
+  if (!mOriginsHavingData) {
+    mOriginsHavingData = new nsTHashtable<nsCStringHashKey>;
+  }
+
+  return *mOriginsHavingData;
+}
+
+nsresult
+DOMStorageDBChild::Init()
+{
+  ContentChild* child = ContentChild::GetSingleton();
+  AddIPDLReference();
+  child->SendPStorageConstructor(this);
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBChild::Shutdown()
+{
+  // There is nothing to do here, IPC will release automatically and
+  // the actual thread running on the parent process will also stop
+  // automatically in profile-before-change topic observer.
+  return NS_OK;
+}
+
+void
+DOMStorageDBChild::AsyncPreload(DOMStorageCacheBridge* aCache, bool aPriority)
+{
+  if (mIPCOpen) {
+    // Adding ref to cache for the time of preload.  This ensures a reference to
+    // to the cache and that all keys will load into this cache object.
+    mLoadingCaches.PutEntry(aCache);
+    SendAsyncPreload(aCache->OriginSuffix(), aCache->OriginNoSuffix(), aPriority);
+  } else {
+    // No IPC, no love.  But the LoadDone call is expected.
+    aCache->LoadDone(NS_ERROR_UNEXPECTED);
+  }
+}
+
+void
+DOMStorageDBChild::AsyncGetUsage(DOMStorageUsageBridge* aUsage)
+{
+  if (mIPCOpen) {
+    SendAsyncGetUsage(aUsage->OriginScope());
+  }
+}
+
+void
+DOMStorageDBChild::SyncPreload(DOMStorageCacheBridge* aCache, bool aForceSync)
+{
+  if (NS_FAILED(mStatus)) {
+    aCache->LoadDone(mStatus);
+    return;
+  }
+
+  if (!mIPCOpen) {
+    aCache->LoadDone(NS_ERROR_UNEXPECTED);
+    return;
+  }
+
+  // There is no way to put the child process to a wait state to receive all
+  // incoming async responses from the parent, hence we have to do a sync preload
+  // instead.  We are smart though, we only demand keys that are left to load in
+  // case the async preload has already loaded some keys.
+  InfallibleTArray<nsString> keys, values;
+  nsresult rv;
+  SendPreload(aCache->OriginSuffix(), aCache->OriginNoSuffix(), aCache->LoadedCount(),
+              &keys, &values, &rv);
+
+  for (uint32_t i = 0; i < keys.Length(); ++i) {
+    aCache->LoadItem(keys[i], values[i]);
+  }
+
+  aCache->LoadDone(rv);
+}
+
+nsresult
+DOMStorageDBChild::AsyncAddItem(DOMStorageCacheBridge* aCache,
+                                const nsAString& aKey,
+                                const nsAString& aValue)
+{
+  if (NS_FAILED(mStatus) || !mIPCOpen) {
+    return mStatus;
+  }
+
+  SendAsyncAddItem(aCache->OriginSuffix(), aCache->OriginNoSuffix(),
+                   nsString(aKey), nsString(aValue));
+  OriginsHavingData().PutEntry(aCache->Origin());
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBChild::AsyncUpdateItem(DOMStorageCacheBridge* aCache,
+                                   const nsAString& aKey,
+                                   const nsAString& aValue)
+{
+  if (NS_FAILED(mStatus) || !mIPCOpen) {
+    return mStatus;
+  }
+
+  SendAsyncUpdateItem(aCache->OriginSuffix(), aCache->OriginNoSuffix(),
+                      nsString(aKey), nsString(aValue));
+  OriginsHavingData().PutEntry(aCache->Origin());
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBChild::AsyncRemoveItem(DOMStorageCacheBridge* aCache,
+                                   const nsAString& aKey)
+{
+  if (NS_FAILED(mStatus) || !mIPCOpen) {
+    return mStatus;
+  }
+
+  SendAsyncRemoveItem(aCache->OriginSuffix(), aCache->OriginNoSuffix(),
+                      nsString(aKey));
+  return NS_OK;
+}
+
+nsresult
+DOMStorageDBChild::AsyncClear(DOMStorageCacheBridge* aCache)
+{
+  if (NS_FAILED(mStatus) || !mIPCOpen) {
+    return mStatus;
+  }
+
+  SendAsyncClear(aCache->OriginSuffix(), aCache->OriginNoSuffix());
+  OriginsHavingData().RemoveEntry(aCache->Origin());
+  return NS_OK;
+}
+
+bool
+DOMStorageDBChild::ShouldPreloadOrigin(const nsACString& aOrigin)
+{
+  // Return true if we didn't receive the origins list yet.
+  // I tend to rather preserve a bit of early-after-start performance
+  // than a bit of memory here.
+  return !mOriginsHavingData || mOriginsHavingData->Contains(aOrigin);
+}
+
+bool
+DOMStorageDBChild::RecvObserve(const nsCString& aTopic,
+                               const nsString& aOriginAttributesPattern,
+                               const nsCString& aOriginScope)
+{
+  DOMStorageObserver::Self()->Notify(
+    aTopic.get(), aOriginAttributesPattern, aOriginScope);
+  return true;
+}
+
+bool
+DOMStorageDBChild::RecvOriginsHavingData(nsTArray<nsCString>&& aOrigins)
+{
+  for (uint32_t i = 0; i < aOrigins.Length(); ++i) {
+    OriginsHavingData().PutEntry(aOrigins[i]);
+  }
+
+  return true;
+}
+
+bool
+DOMStorageDBChild::RecvLoadItem(const nsCString& aOriginSuffix,
+                                const nsCString& aOriginNoSuffix,
+                                const nsString& aKey,
+                                const nsString& aValue)
+{
+  DOMStorageCache* aCache = mManager->GetCache(aOriginSuffix, aOriginNoSuffix);
+  if (aCache) {
+    aCache->LoadItem(aKey, aValue);
+  }
+
+  return true;
+}
+
+bool
+DOMStorageDBChild::RecvLoadDone(const nsCString& aOriginSuffix,
+                                const nsCString& aOriginNoSuffix,
+                                const nsresult& aRv)
+{
+  DOMStorageCache* aCache = mManager->GetCache(aOriginSuffix, aOriginNoSuffix);
+  if (aCache) {
+    aCache->LoadDone(aRv);
+
+    // Just drop reference to this cache now since the load is done.
+    mLoadingCaches.RemoveEntry(static_cast<DOMStorageCacheBridge*>(aCache));
+  }
+
+  return true;
+}
+
+bool
+DOMStorageDBChild::RecvLoadUsage(const nsCString& aOriginNoSuffix, const int64_t& aUsage)
+{
+  RefPtr<DOMStorageUsageBridge> scopeUsage = mManager->GetOriginUsage(aOriginNoSuffix);
+  scopeUsage->LoadUsage(aUsage);
+  return true;
+}
+
+bool
+DOMStorageDBChild::RecvError(const nsresult& aRv)
+{
+  mStatus = aRv;
+  return true;
+}
+
+// ----------------------------------------------------------------------------
+// Parent
+// ----------------------------------------------------------------------------
+
+NS_IMPL_ADDREF(DOMStorageDBParent)
+NS_IMPL_RELEASE(DOMStorageDBParent)
+
+void
+DOMStorageDBParent::AddIPDLReference()
+{
+  MOZ_ASSERT(!mIPCOpen, "Attempting to retain multiple IPDL references");
+  mIPCOpen = true;
+  AddRef();
+}
+
+void
+DOMStorageDBParent::ReleaseIPDLReference()
+{
+  MOZ_ASSERT(mIPCOpen, "Attempting to release non-existent IPDL reference");
+  mIPCOpen = false;
+  Release();
+}
+
+namespace {
+
+class SendInitialChildDataRunnable : public Runnable
+{
+public:
+  explicit SendInitialChildDataRunnable(DOMStorageDBParent* aParent)
+    : mParent(aParent)
+  {}
+
+private:
+  NS_IMETHOD Run() override
+  {
+    if (!mParent->IPCOpen()) {
+      return NS_OK;
+    }
+
+    DOMStorageDBBridge* db = DOMStorageCache::GetDatabase();
+    if (db) {
+      InfallibleTArray<nsCString> scopes;
+      db->GetOriginsHavingData(&scopes);
+      mozilla::Unused << mParent->SendOriginsHavingData(scopes);
+    }
+
+    // We need to check if the device is in a low disk space situation, so
+    // we can forbid in that case any write in localStorage.
+    nsCOMPtr<nsIDiskSpaceWatcher> diskSpaceWatcher =
+      do_GetService("@mozilla.org/toolkit/disk-space-watcher;1");
+    if (!diskSpaceWatcher) {
+      return NS_OK;
+    }
+
+    bool lowDiskSpace = false;
+    diskSpaceWatcher->GetIsDiskFull(&lowDiskSpace);
+
+    if (lowDiskSpace) {
+      mozilla::Unused << mParent->SendObserve(
+        nsDependentCString("low-disk-space"), EmptyString(), EmptyCString());
+    }
+
+    return NS_OK;
+  }
+
+  RefPtr<DOMStorageDBParent> mParent;
+};
+
+} // namespace
+
+DOMStorageDBParent::DOMStorageDBParent()
+: mIPCOpen(false)
+{
+  DOMStorageObserver* observer = DOMStorageObserver::Self();
+  if (observer) {
+    observer->AddSink(this);
+  }
+
+  // We are always open by IPC only
+  AddIPDLReference();
+
+  // Cannot send directly from here since the channel
+  // is not completely built at this moment.
+  RefPtr<SendInitialChildDataRunnable> r =
+    new SendInitialChildDataRunnable(this);
+  NS_DispatchToCurrentThread(r);
+}
+
+DOMStorageDBParent::~DOMStorageDBParent()
+{
+  DOMStorageObserver* observer = DOMStorageObserver::Self();
+  if (observer) {
+    observer->RemoveSink(this);
+  }
+}
+
+DOMStorageDBParent::CacheParentBridge*
+DOMStorageDBParent::NewCache(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix)
+{
+  return new CacheParentBridge(this, aOriginSuffix, aOriginNoSuffix);
+}
+
+void
+DOMStorageDBParent::ActorDestroy(ActorDestroyReason aWhy)
+{
+  // Implement me! Bug 1005169
+}
+
+bool
+DOMStorageDBParent::RecvAsyncPreload(const nsCString& aOriginSuffix,
+                                     const nsCString& aOriginNoSuffix,
+                                     const bool& aPriority)
+{
+  DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+  if (!db) {
+    return false;
+  }
+
+  db->AsyncPreload(NewCache(aOriginSuffix, aOriginNoSuffix), aPriority);
+  return true;
+}
+
+bool
+DOMStorageDBParent::RecvAsyncGetUsage(const nsCString& aOriginNoSuffix)
+{
+  DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+  if (!db) {
+    return false;
+  }
+
+  // The object releases it self in LoadUsage method
+  RefPtr<UsageParentBridge> usage = new UsageParentBridge(this, aOriginNoSuffix);
+  db->AsyncGetUsage(usage);
+  return true;
+}
+
+namespace {
+
+// We need another implementation of DOMStorageCacheBridge to do
+// synchronous IPC preload.  This class just receives Load* notifications
+// and fills the returning arguments of RecvPreload with the database
+// values for us.
+class SyncLoadCacheHelper : public DOMStorageCacheBridge
+{
+public:
+  SyncLoadCacheHelper(const nsCString& aOriginSuffix,
+                      const nsCString& aOriginNoSuffix,
+                      uint32_t aAlreadyLoadedCount,
+                      InfallibleTArray<nsString>* aKeys,
+                      InfallibleTArray<nsString>* aValues,
+                      nsresult* rv)
+  : mMonitor("DOM Storage SyncLoad IPC")
+  , mSuffix(aOriginSuffix)
+  , mOrigin(aOriginNoSuffix)
+  , mKeys(aKeys)
+  , mValues(aValues)
+  , mRv(rv)
+  , mLoaded(false)
+  , mLoadedCount(aAlreadyLoadedCount)
+  {
+    // Precaution
+    *mRv = NS_ERROR_UNEXPECTED;
+  }
+
+  virtual const nsCString Origin() const
+  {
+    return DOMStorageManager::CreateOrigin(mSuffix, mOrigin);
+  }
+  virtual const nsCString& OriginNoSuffix() const { return mOrigin; }
+  virtual const nsCString& OriginSuffix() const { return mSuffix; }
+  virtual bool Loaded() { return mLoaded; }
+  virtual uint32_t LoadedCount() { return mLoadedCount; }
+  virtual bool LoadItem(const nsAString& aKey, const nsString& aValue)
+  {
+    // Called on the aCache background thread
+    MOZ_ASSERT(!mLoaded);
+    if (mLoaded) {
+      return false;
+    }
+
+    ++mLoadedCount;
+    mKeys->AppendElement(aKey);
+    mValues->AppendElement(aValue);
+    return true;
+  }
+
+  virtual void LoadDone(nsresult aRv)
+  {
+    // Called on the aCache background thread
+    MonitorAutoLock monitor(mMonitor);
+    MOZ_ASSERT(!mLoaded && mRv);
+    mLoaded = true;
+    if (mRv) {
+      *mRv = aRv;
+      mRv = nullptr;
+    }
+    monitor.Notify();
+  }
+
+  virtual void LoadWait()
+  {
+    // Called on the main thread, exits after LoadDone() call
+    MonitorAutoLock monitor(mMonitor);
+    while (!mLoaded) {
+      monitor.Wait();
+    }
+  }
+
+private:
+  Monitor mMonitor;
+  nsCString mSuffix, mOrigin;
+  InfallibleTArray<nsString>* mKeys;
+  InfallibleTArray<nsString>* mValues;
+  nsresult* mRv;
+  bool mLoaded;
+  uint32_t mLoadedCount;
+};
+
+} // namespace
+
+bool
+DOMStorageDBParent::RecvPreload(const nsCString& aOriginSuffix,
+                                const nsCString& aOriginNoSuffix,
+                                const uint32_t& aAlreadyLoadedCount,
+                                InfallibleTArray<nsString>* aKeys,
+                                InfallibleTArray<nsString>* aValues,
+                                nsresult* aRv)
+{
+  DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+  if (!db) {
+    return false;
+  }
+
+  RefPtr<SyncLoadCacheHelper> cache(
+    new SyncLoadCacheHelper(aOriginSuffix, aOriginNoSuffix, aAlreadyLoadedCount, aKeys, aValues, aRv));
+
+  db->SyncPreload(cache, true);
+  return true;
+}
+
+bool
+DOMStorageDBParent::RecvAsyncAddItem(const nsCString& aOriginSuffix,
+                                     const nsCString& aOriginNoSuffix,
+                                     const nsString& aKey,
+                                     const nsString& aValue)
+{
+  DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+  if (!db) {
+    return false;
+  }
+
+  nsresult rv = db->AsyncAddItem(NewCache(aOriginSuffix, aOriginNoSuffix), aKey, aValue);
+  if (NS_FAILED(rv) && mIPCOpen) {
+    mozilla::Unused << SendError(rv);
+  }
+
+  return true;
+}
+
+bool
+DOMStorageDBParent::RecvAsyncUpdateItem(const nsCString& aOriginSuffix,
+                                        const nsCString& aOriginNoSuffix,
+                                        const nsString& aKey,
+                                        const nsString& aValue)
+{
+  DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+  if (!db) {
+    return false;
+  }
+
+  nsresult rv = db->AsyncUpdateItem(NewCache(aOriginSuffix, aOriginNoSuffix), aKey, aValue);
+  if (NS_FAILED(rv) && mIPCOpen) {
+    mozilla::Unused << SendError(rv);
+  }
+
+  return true;
+}
+
+bool
+DOMStorageDBParent::RecvAsyncRemoveItem(const nsCString& aOriginSuffix,
+                                        const nsCString& aOriginNoSuffix,
+                                        const nsString& aKey)
+{
+  DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+  if (!db) {
+    return false;
+  }
+
+  nsresult rv = db->AsyncRemoveItem(NewCache(aOriginSuffix, aOriginNoSuffix), aKey);
+  if (NS_FAILED(rv) && mIPCOpen) {
+    mozilla::Unused << SendError(rv);
+  }
+
+  return true;
+}
+
+bool
+DOMStorageDBParent::RecvAsyncClear(const nsCString& aOriginSuffix,
+                                   const nsCString& aOriginNoSuffix)
+{
+  DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+  if (!db) {
+    return false;
+  }
+
+  nsresult rv = db->AsyncClear(NewCache(aOriginSuffix, aOriginNoSuffix));
+  if (NS_FAILED(rv) && mIPCOpen) {
+    mozilla::Unused << SendError(rv);
+  }
+
+  return true;
+}
+
+bool
+DOMStorageDBParent::RecvAsyncFlush()
+{
+  DOMStorageDBBridge* db = DOMStorageCache::GetDatabase();
+  if (!db) {
+    return false;
+  }
+
+  db->AsyncFlush();
+  return true;
+}
+
+// DOMStorageObserverSink
+
+nsresult
+DOMStorageDBParent::Observe(const char* aTopic,
+                            const nsAString& aOriginAttributesPattern,
+                            const nsACString& aOriginScope)
+{
+  if (mIPCOpen) {
+      mozilla::Unused << SendObserve(nsDependentCString(aTopic),
+                                     nsString(aOriginAttributesPattern),
+                                     nsCString(aOriginScope));
+  }
+
+  return NS_OK;
+}
+
+namespace {
+
+// Results must be sent back on the main thread
+class LoadRunnable : public Runnable
+{
+public:
+  enum TaskType {
+    loadItem,
+    loadDone
+  };
+
+  LoadRunnable(DOMStorageDBParent* aParent,
+               TaskType aType,
+               const nsACString& aOriginSuffix,
+               const nsACString& aOriginNoSuffix,
+               const nsAString& aKey = EmptyString(),
+               const nsAString& aValue = EmptyString())
+  : mParent(aParent)
+  , mType(aType)
+  , mSuffix(aOriginSuffix)
+  , mOrigin(aOriginNoSuffix)
+  , mKey(aKey)
+  , mValue(aValue)
+  { }
+
+  LoadRunnable(DOMStorageDBParent* aParent,
+               TaskType aType,
+               const nsACString& aOriginSuffix,
+               const nsACString& aOriginNoSuffix,
+               nsresult aRv)
+  : mParent(aParent)
+  , mType(aType)
+  , mSuffix(aOriginSuffix)
+  , mOrigin(aOriginNoSuffix)
+  , mRv(aRv)
+  { }
+
+private:
+  RefPtr<DOMStorageDBParent> mParent;
+  TaskType mType;
+  nsCString mSuffix, mOrigin;
+  nsString mKey;
+  nsString mValue;
+  nsresult mRv;
+
+  NS_IMETHOD Run() override
+  {
+    if (!mParent->IPCOpen()) {
+      return NS_OK;
+    }
+
+    switch (mType)
+    {
+    case loadItem:
+      mozilla::Unused << mParent->SendLoadItem(mSuffix, mOrigin, mKey, mValue);
+      break;
+    case loadDone:
+      mozilla::Unused << mParent->SendLoadDone(mSuffix, mOrigin, mRv);
+      break;
+    }
+
+    return NS_OK;
+  }
+};
+
+} // namespace
+
+// DOMStorageDBParent::CacheParentBridge
+
+const nsCString
+DOMStorageDBParent::CacheParentBridge::Origin() const
+{
+  return DOMStorageManager::CreateOrigin(mOriginSuffix, mOriginNoSuffix);
+}
+
+bool
+DOMStorageDBParent::CacheParentBridge::LoadItem(const nsAString& aKey, const nsString& aValue)
+{
+  if (mLoaded) {
+    return false;
+  }
+
+  ++mLoadedCount;
+
+  RefPtr<LoadRunnable> r =
+    new LoadRunnable(mParent, LoadRunnable::loadItem, mOriginSuffix, mOriginNoSuffix, aKey, aValue);
+  NS_DispatchToMainThread(r);
+  return true;
+}
+
+void
+DOMStorageDBParent::CacheParentBridge::LoadDone(nsresult aRv)
+{
+  // Prevent send of duplicate LoadDone.
+  if (mLoaded) {
+    return;
+  }
+
+  mLoaded = true;
+
+  RefPtr<LoadRunnable> r =
+    new LoadRunnable(mParent, LoadRunnable::loadDone, mOriginSuffix, mOriginNoSuffix, aRv);
+  NS_DispatchToMainThread(r);
+}
+
+void
+DOMStorageDBParent::CacheParentBridge::LoadWait()
+{
+  // Should never be called on this implementation
+  MOZ_ASSERT(false);
+}
+
+// DOMStorageDBParent::UsageParentBridge
+
+namespace {
+
+class UsageRunnable : public Runnable
+{
+public:
+  UsageRunnable(DOMStorageDBParent* aParent, const nsACString& aOriginScope, const int64_t& aUsage)
+  : mParent(aParent)
+  , mOriginScope(aOriginScope)
+  , mUsage(aUsage)
+  {}
+
+private:
+  NS_IMETHOD Run() override
+  {
+    if (!mParent->IPCOpen()) {
+      return NS_OK;
+    }
+
+    mozilla::Unused << mParent->SendLoadUsage(mOriginScope, mUsage);
+    return NS_OK;
+  }
+
+  RefPtr<DOMStorageDBParent> mParent;
+  nsCString mOriginScope;
+  int64_t mUsage;
+};
+
+} // namespace
+
+void
+DOMStorageDBParent::UsageParentBridge::LoadUsage(const int64_t aUsage)
+{
+  RefPtr<UsageRunnable> r = new UsageRunnable(mParent, mOriginScope, aUsage);
+  NS_DispatchToMainThread(r);
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/DOMStorageIPC.h b/dom/storage/DOMStorageIPC.h
new file mode 100644
index 0000000000..b3508a5880
--- /dev/null
+++ b/dom/storage/DOMStorageIPC.h
@@ -0,0 +1,218 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 nsDOMStorageIPC_h___
+#define nsDOMStorageIPC_h___
+
+#include "mozilla/dom/PStorageChild.h"
+#include "mozilla/dom/PStorageParent.h"
+#include "DOMStorageDBThread.h"
+#include "DOMStorageCache.h"
+#include "DOMStorageObserver.h"
+#include "mozilla/Mutex.h"
+#include "nsAutoPtr.h"
+
+namespace mozilla {
+
+class OriginAttributesPattern;
+
+namespace dom {
+
+class DOMLocalStorageManager;
+
+// Child side of the IPC protocol, exposes as DB interface but
+// is responsible to send all requests to the parent process
+// and expects asynchronous answers. Those are then transparently
+// forwarded back to consumers on the child process.
+class DOMStorageDBChild final : public DOMStorageDBBridge
+                              , public PStorageChild
+{
+  virtual ~DOMStorageDBChild();
+
+public:
+  explicit DOMStorageDBChild(DOMLocalStorageManager* aManager);
+
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void);
+  NS_IMETHOD_(MozExternalRefCountType) Release(void);
+
+  void AddIPDLReference();
+  void ReleaseIPDLReference();
+
+  virtual nsresult Init();
+  virtual nsresult Shutdown();
+
+  virtual void AsyncPreload(DOMStorageCacheBridge* aCache, bool aPriority = false);
+  virtual void AsyncGetUsage(DOMStorageUsageBridge* aUsage);
+
+  virtual void SyncPreload(DOMStorageCacheBridge* aCache, bool aForceSync = false);
+
+  virtual nsresult AsyncAddItem(DOMStorageCacheBridge* aCache, const nsAString& aKey, const nsAString& aValue);
+  virtual nsresult AsyncUpdateItem(DOMStorageCacheBridge* aCache, const nsAString& aKey, const nsAString& aValue);
+  virtual nsresult AsyncRemoveItem(DOMStorageCacheBridge* aCache, const nsAString& aKey);
+  virtual nsresult AsyncClear(DOMStorageCacheBridge* aCache);
+
+  virtual void AsyncClearAll()
+  {
+    if (mOriginsHavingData) {
+      mOriginsHavingData->Clear(); /* NO-OP on the child process otherwise */
+    }
+  }
+
+  virtual void AsyncClearMatchingOrigin(const nsACString& aOriginNoSuffix)
+    { /* NO-OP on the child process */ }
+
+  virtual void AsyncClearMatchingOriginAttributes(const OriginAttributesPattern& aPattern)
+    { /* NO-OP on the child process */ }
+
+  virtual void AsyncFlush()
+    { SendAsyncFlush(); }
+
+  virtual bool ShouldPreloadOrigin(const nsACString& aOriginNoSuffix);
+  virtual void GetOriginsHavingData(InfallibleTArray<nsCString>* aOrigins)
+    { NS_NOTREACHED("Not implemented for child process"); }
+
+private:
+  bool RecvObserve(const nsCString& aTopic,
+                   const nsString& aOriginAttributesPattern,
+                   const nsCString& aOriginScope);
+  bool RecvLoadItem(const nsCString& aOriginSuffix,
+                    const nsCString& aOriginNoSuffix,
+                    const nsString& aKey,
+                    const nsString& aValue);
+  bool RecvLoadDone(const nsCString& aOriginSuffix,
+                    const nsCString& aOriginNoSuffix,
+                    const nsresult& aRv);
+  bool RecvOriginsHavingData(nsTArray<nsCString>&& aOrigins);
+  bool RecvLoadUsage(const nsCString& aOriginNoSuffix,
+                     const int64_t& aUsage);
+  bool RecvError(const nsresult& aRv);
+
+  nsTHashtable<nsCStringHashKey>& OriginsHavingData();
+
+  ThreadSafeAutoRefCnt mRefCnt;
+  NS_DECL_OWNINGTHREAD
+
+  // Held to get caches to forward answers to.
+  RefPtr<DOMLocalStorageManager> mManager;
+
+  // Origins having data hash, for optimization purposes only
+  nsAutoPtr<nsTHashtable<nsCStringHashKey>> mOriginsHavingData;
+
+  // List of caches waiting for preload.  This ensures the contract that
+  // AsyncPreload call references the cache for time of the preload.
+  nsTHashtable<nsRefPtrHashKey<DOMStorageCacheBridge>> mLoadingCaches;
+
+  // Status of the remote database
+  nsresult mStatus;
+
+  bool mIPCOpen;
+};
+
+
+// Receives async requests from child processes and is responsible
+// to send back responses from the DB thread.  Exposes as a fake
+// DOMStorageCache consumer.
+// Also responsible for forwardning all chrome operation notifications
+// such as cookie cleaning etc to the child process.
+class DOMStorageDBParent final : public PStorageParent
+                               , public DOMStorageObserverSink
+{
+  virtual ~DOMStorageDBParent();
+
+public:
+  DOMStorageDBParent();
+
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void);
+  NS_IMETHOD_(MozExternalRefCountType) Release(void);
+
+  void AddIPDLReference();
+  void ReleaseIPDLReference();
+
+  bool IPCOpen() { return mIPCOpen; }
+
+public:
+  // Fake cache class receiving async callbacks from DB thread, sending
+  // them back to appropriate cache object on the child process.
+  class CacheParentBridge : public DOMStorageCacheBridge {
+  public:
+    CacheParentBridge(DOMStorageDBParent* aParentDB,
+                      const nsACString& aOriginSuffix,
+                      const nsACString& aOriginNoSuffix)
+      : mParent(aParentDB)
+      , mOriginSuffix(aOriginSuffix), mOriginNoSuffix(aOriginNoSuffix)
+      , mLoaded(false), mLoadedCount(0) {}
+    virtual ~CacheParentBridge() {}
+
+    // DOMStorageCacheBridge
+    virtual const nsCString Origin() const;
+    virtual const nsCString& OriginNoSuffix() const
+      { return mOriginNoSuffix; }
+    virtual const nsCString& OriginSuffix() const
+      { return mOriginSuffix; }
+    virtual bool Loaded()
+      { return mLoaded; }
+    virtual uint32_t LoadedCount()
+      { return mLoadedCount; }
+
+    virtual bool LoadItem(const nsAString& aKey, const nsString& aValue);
+    virtual void LoadDone(nsresult aRv);
+    virtual void LoadWait();
+
+  private:
+    RefPtr<DOMStorageDBParent> mParent;
+    nsCString mOriginSuffix, mOriginNoSuffix;
+    bool mLoaded;
+    uint32_t mLoadedCount;
+  };
+
+  // Fake usage class receiving async callbacks from DB thread
+  class UsageParentBridge : public DOMStorageUsageBridge
+  {
+  public:
+    UsageParentBridge(DOMStorageDBParent* aParentDB, const nsACString& aOriginScope)
+      : mParent(aParentDB), mOriginScope(aOriginScope) {}
+    virtual ~UsageParentBridge() {}
+
+    // DOMStorageUsageBridge
+    virtual const nsCString& OriginScope() { return mOriginScope; }
+    virtual void LoadUsage(const int64_t usage);
+
+  private:
+    RefPtr<DOMStorageDBParent> mParent;
+    nsCString mOriginScope;
+  };
+
+private:
+  // IPC
+  virtual void ActorDestroy(ActorDestroyReason aWhy) override;
+  bool RecvAsyncPreload(const nsCString& aOriginSuffix, const nsCString& aOriginNoSuffix, const bool& aPriority) override;
+  bool RecvPreload(const nsCString& aOriginSuffix, const nsCString& aOriginNoSuffix, const uint32_t& aAlreadyLoadedCount,
+                   InfallibleTArray<nsString>* aKeys, InfallibleTArray<nsString>* aValues,
+                   nsresult* aRv) override;
+  bool RecvAsyncGetUsage(const nsCString& aOriginNoSuffix) override;
+  bool RecvAsyncAddItem(const nsCString& aOriginSuffix, const nsCString& aOriginNoSuffix, const nsString& aKey, const nsString& aValue) override;
+  bool RecvAsyncUpdateItem(const nsCString& aOriginSuffix, const nsCString& aOriginNoSuffix, const nsString& aKey, const nsString& aValue) override;
+  bool RecvAsyncRemoveItem(const nsCString& aOriginSuffix, const nsCString& aOriginNoSuffix, const nsString& aKey) override;
+  bool RecvAsyncClear(const nsCString& aOriginSuffix, const nsCString& aOriginNoSuffix) override;
+  bool RecvAsyncFlush() override;
+
+  // DOMStorageObserverSink
+  virtual nsresult Observe(const char* aTopic, const nsAString& aOriginAttrPattern, const nsACString& aOriginScope) override;
+
+private:
+  CacheParentBridge* NewCache(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix);
+
+  ThreadSafeAutoRefCnt mRefCnt;
+  NS_DECL_OWNINGTHREAD
+
+  // True when IPC channel is open and Send*() methods are OK to use.
+  bool mIPCOpen;
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif
diff --git a/dom/storage/DOMStorageManager.cpp b/dom/storage/DOMStorageManager.cpp
new file mode 100644
index 0000000000..156e846ba9
--- /dev/null
+++ b/dom/storage/DOMStorageManager.cpp
@@ -0,0 +1,661 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "DOMStorageManager.h"
+#include "DOMStorage.h"
+#include "DOMStorageDBThread.h"
+
+#include "nsIScriptSecurityManager.h"
+#include "nsIEffectiveTLDService.h"
+
+#include "nsNetUtil.h"
+#include "nsNetCID.h"
+#include "nsIURL.h"
+#include "nsPrintfCString.h"
+#include "nsXULAppAPI.h"
+#include "nsThreadUtils.h"
+#include "nsIObserverService.h"
+#include "mozilla/Services.h"
+#include "mozilla/Preferences.h"
+
+// Only allow relatively small amounts of data since performance of
+// the synchronous IO is very bad.
+// We are enforcing simple per-origin quota only.
+#define DEFAULT_QUOTA_LIMIT (5 * 1024)
+
+namespace mozilla {
+namespace dom {
+
+namespace {
+
+int32_t gQuotaLimit = DEFAULT_QUOTA_LIMIT;
+
+} // namespace
+
+DOMLocalStorageManager*
+DOMLocalStorageManager::sSelf = nullptr;
+
+// static
+uint32_t
+DOMStorageManager::GetQuota()
+{
+  static bool preferencesInitialized = false;
+  if (!preferencesInitialized) {
+    mozilla::Preferences::AddIntVarCache(&gQuotaLimit, "dom.storage.default_quota",
+                                         DEFAULT_QUOTA_LIMIT);
+    preferencesInitialized = true;
+  }
+
+  return gQuotaLimit * 1024; // pref is in kBs
+}
+
+void
+ReverseString(const nsCSubstring& aSource, nsCSubstring& aResult)
+{
+  nsACString::const_iterator sourceBegin, sourceEnd;
+  aSource.BeginReading(sourceBegin);
+  aSource.EndReading(sourceEnd);
+
+  aResult.SetLength(aSource.Length());
+  nsACString::iterator destEnd;
+  aResult.EndWriting(destEnd);
+
+  while (sourceBegin != sourceEnd) {
+    *(--destEnd) = *sourceBegin;
+    ++sourceBegin;
+  }
+}
+
+nsresult
+CreateReversedDomain(const nsACString& aAsciiDomain,
+                     nsACString& aKey)
+{
+  if (aAsciiDomain.IsEmpty()) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  ReverseString(aAsciiDomain, aKey);
+
+  aKey.Append('.');
+  return NS_OK;
+}
+
+bool
+PrincipalsEqual(nsIPrincipal* aObjectPrincipal, nsIPrincipal* aSubjectPrincipal)
+{
+  if (!aSubjectPrincipal) {
+    return true;
+  }
+
+  if (!aObjectPrincipal) {
+    return false;
+  }
+
+  return aSubjectPrincipal->Equals(aObjectPrincipal);
+}
+
+NS_IMPL_ISUPPORTS(DOMStorageManager,
+                  nsIDOMStorageManager)
+
+DOMStorageManager::DOMStorageManager(DOMStorage::StorageType aType)
+  : mCaches(8)
+  , mType(aType)
+  , mLowDiskSpace(false)
+{
+  DOMStorageObserver* observer = DOMStorageObserver::Self();
+  NS_ASSERTION(observer, "No DOMStorageObserver, cannot observe private data delete notifications!");
+
+  if (observer) {
+    observer->AddSink(this);
+  }
+}
+
+DOMStorageManager::~DOMStorageManager()
+{
+  DOMStorageObserver* observer = DOMStorageObserver::Self();
+  if (observer) {
+    observer->RemoveSink(this);
+  }
+}
+
+namespace {
+
+nsresult
+AppendOriginNoSuffix(nsIPrincipal* aPrincipal,
+                nsACString& aKey)
+{
+  nsresult rv;
+
+  nsCOMPtr<nsIURI> uri;
+  rv = aPrincipal->GetURI(getter_AddRefs(uri));
+  NS_ENSURE_SUCCESS(rv, rv);
+  if (!uri) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsAutoCString domainOrigin;
+  rv = uri->GetAsciiHost(domainOrigin);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (domainOrigin.IsEmpty()) {
+    // For the file:/// protocol use the exact directory as domain.
+    bool isScheme = false;
+    if (NS_SUCCEEDED(uri->SchemeIs("file", &isScheme)) && isScheme) {
+      nsCOMPtr<nsIURL> url = do_QueryInterface(uri, &rv);
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = url->GetDirectory(domainOrigin);
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+  }
+
+  // Append reversed domain
+  nsAutoCString reverseDomain;
+  rv = CreateReversedDomain(domainOrigin, reverseDomain);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  aKey.Append(reverseDomain);
+
+  // Append scheme
+  nsAutoCString scheme;
+  rv = uri->GetScheme(scheme);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  aKey.Append(':');
+  aKey.Append(scheme);
+
+  // Append port if any
+  int32_t port = NS_GetRealPort(uri);
+  if (port != -1) {
+    aKey.Append(nsPrintfCString(":%d", port));
+  }
+
+  return NS_OK;
+}
+
+nsresult
+CreateQuotaDBKey(nsIPrincipal* aPrincipal,
+                 nsACString& aKey)
+{
+  nsresult rv;
+
+  nsCOMPtr<nsIEffectiveTLDService> eTLDService(do_GetService(
+    NS_EFFECTIVETLDSERVICE_CONTRACTID, &rv));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIURI> uri;
+  rv = aPrincipal->GetURI(getter_AddRefs(uri));
+  NS_ENSURE_SUCCESS(rv, rv);
+  NS_ENSURE_TRUE(uri, NS_ERROR_UNEXPECTED);
+
+  nsAutoCString eTLDplusOne;
+  rv = eTLDService->GetBaseDomain(uri, 0, eTLDplusOne);
+  if (NS_ERROR_INSUFFICIENT_DOMAIN_LEVELS == rv) {
+    // XXX bug 357323 - what to do for localhost/file exactly?
+    rv = uri->GetAsciiHost(eTLDplusOne);
+  }
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  aKey.Truncate();
+  BasePrincipal::Cast(aPrincipal)->OriginAttributesRef().CreateSuffix(aKey);
+
+  nsAutoCString subdomainsDBKey;
+  CreateReversedDomain(eTLDplusOne, subdomainsDBKey);
+
+  aKey.Append(':');
+  aKey.Append(subdomainsDBKey);
+
+  return NS_OK;
+}
+
+} // namespace
+
+// static
+nsCString
+DOMStorageManager::CreateOrigin(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix)
+{
+  // Note: some hard-coded sqlite statements are dependent on the format this
+  // method returns.  Changing this without updating those sqlite statements
+  // will cause malfunction.
+
+  nsAutoCString scope;
+  scope.Append(aOriginSuffix);
+  scope.Append(':');
+  scope.Append(aOriginNoSuffix);
+  return scope;
+}
+
+DOMStorageCache*
+DOMStorageManager::GetCache(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix)
+{
+  CacheOriginHashtable* table = mCaches.LookupOrAdd(aOriginSuffix);
+  DOMStorageCacheHashKey* entry = table->GetEntry(aOriginNoSuffix);
+  if (!entry) {
+    return nullptr;
+  }
+
+  return entry->cache();
+}
+
+already_AddRefed<DOMStorageUsage>
+DOMStorageManager::GetOriginUsage(const nsACString& aOriginNoSuffix)
+{
+  RefPtr<DOMStorageUsage> usage;
+  if (mUsages.Get(aOriginNoSuffix, &usage)) {
+    return usage.forget();
+  }
+
+  usage = new DOMStorageUsage(aOriginNoSuffix);
+
+  if (mType == LocalStorage) {
+    DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+    if (db) {
+      db->AsyncGetUsage(usage);
+    }
+  }
+
+  mUsages.Put(aOriginNoSuffix, usage);
+
+  return usage.forget();
+}
+
+already_AddRefed<DOMStorageCache>
+DOMStorageManager::PutCache(const nsACString& aOriginSuffix,
+                            const nsACString& aOriginNoSuffix,
+                            nsIPrincipal* aPrincipal)
+{
+  CacheOriginHashtable* table = mCaches.LookupOrAdd(aOriginSuffix);
+  DOMStorageCacheHashKey* entry = table->PutEntry(aOriginNoSuffix);
+  RefPtr<DOMStorageCache> cache = entry->cache();
+
+  nsAutoCString quotaOrigin;
+  CreateQuotaDBKey(aPrincipal, quotaOrigin);
+
+  switch (mType) {
+  case SessionStorage:
+    // Lifetime handled by the manager, don't persist
+    entry->HardRef();
+    cache->Init(this, false, aPrincipal, quotaOrigin);
+    break;
+
+  case LocalStorage:
+    // Lifetime handled by the cache, do persist
+    cache->Init(this, true, aPrincipal, quotaOrigin);
+    break;
+
+  default:
+    MOZ_ASSERT(false);
+  }
+
+  return cache.forget();
+}
+
+void
+DOMStorageManager::DropCache(DOMStorageCache* aCache)
+{
+  if (!NS_IsMainThread()) {
+    NS_WARNING("DOMStorageManager::DropCache called on a non-main thread, shutting down?");
+  }
+
+  CacheOriginHashtable* table = mCaches.LookupOrAdd(aCache->OriginSuffix());
+  table->RemoveEntry(aCache->OriginNoSuffix());
+}
+
+nsresult
+DOMStorageManager::GetStorageInternal(bool aCreate,
+                                      mozIDOMWindow* aWindow,
+                                      nsIPrincipal* aPrincipal,
+                                      const nsAString& aDocumentURI,
+                                      bool aPrivate,
+                                      nsIDOMStorage** aRetval)
+{
+  nsresult rv;
+
+  nsAutoCString originAttrSuffix;
+  BasePrincipal::Cast(aPrincipal)->OriginAttributesRef().CreateSuffix(originAttrSuffix);
+
+  nsAutoCString originKey;
+  rv = AppendOriginNoSuffix(aPrincipal, originKey);
+  if (NS_FAILED(rv)) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  RefPtr<DOMStorageCache> cache = GetCache(originAttrSuffix, originKey);
+
+  // Get or create a cache for the given scope
+  if (!cache) {
+    if (!aCreate) {
+      *aRetval = nullptr;
+      return NS_OK;
+    }
+
+    if (!aRetval) {
+      // This is a demand to just preload the cache, if the scope has
+      // no data stored, bypass creation and preload of the cache.
+      DOMStorageDBBridge* db = DOMStorageCache::GetDatabase();
+      if (db) {
+        if (!db->ShouldPreloadOrigin(DOMStorageManager::CreateOrigin(originAttrSuffix, originKey))) {
+          return NS_OK;
+        }
+      } else {
+        if (originKey.EqualsLiteral("knalb.:about")) {
+          return NS_OK;
+        }
+      }
+    }
+
+    // There is always a single instance of a cache per scope
+    // in a single instance of a DOM storage manager.
+    cache = PutCache(originAttrSuffix, originKey, aPrincipal);
+  } else if (mType == SessionStorage) {
+    if (!cache->CheckPrincipal(aPrincipal)) {
+      return NS_ERROR_DOM_SECURITY_ERR;
+    }
+  }
+
+  if (aRetval) {
+    nsCOMPtr<nsPIDOMWindowInner> inner = nsPIDOMWindowInner::From(aWindow);
+
+    nsCOMPtr<nsIDOMStorage> storage = new DOMStorage(
+      inner, this, cache, aDocumentURI, aPrincipal, aPrivate);
+    storage.forget(aRetval);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+DOMStorageManager::PrecacheStorage(nsIPrincipal* aPrincipal)
+{
+  return GetStorageInternal(true, nullptr, aPrincipal, EmptyString(), false,
+                            nullptr);
+}
+
+NS_IMETHODIMP
+DOMStorageManager::CreateStorage(mozIDOMWindow* aWindow,
+                                 nsIPrincipal* aPrincipal,
+                                 const nsAString& aDocumentURI,
+                                 bool aPrivate,
+                                 nsIDOMStorage** aRetval)
+{
+  return GetStorageInternal(true, aWindow, aPrincipal, aDocumentURI, aPrivate,
+                            aRetval);
+}
+
+NS_IMETHODIMP
+DOMStorageManager::GetStorage(mozIDOMWindow* aWindow,
+                              nsIPrincipal* aPrincipal,
+                              bool aPrivate,
+                              nsIDOMStorage** aRetval)
+{
+  return GetStorageInternal(false, aWindow, aPrincipal, EmptyString(), aPrivate,
+                            aRetval);
+}
+
+NS_IMETHODIMP
+DOMStorageManager::CloneStorage(nsIDOMStorage* aStorage)
+{
+  if (mType != SessionStorage) {
+    // Cloning is supported only for sessionStorage
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  RefPtr<DOMStorage> storage = static_cast<DOMStorage*>(aStorage);
+  if (!storage) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  const DOMStorageCache* origCache = storage->GetCache();
+
+  DOMStorageCache* existingCache = GetCache(origCache->OriginSuffix(),
+                                            origCache->OriginNoSuffix());
+  if (existingCache) {
+    // Do not replace an existing sessionStorage.
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  // Since this manager is sessionStorage manager, PutCache hard references
+  // the cache in our hashtable.
+  RefPtr<DOMStorageCache> newCache = PutCache(origCache->OriginSuffix(),
+                                              origCache->OriginNoSuffix(),
+                                              origCache->Principal());
+
+  newCache->CloneFrom(origCache);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+DOMStorageManager::CheckStorage(nsIPrincipal* aPrincipal,
+                                nsIDOMStorage* aStorage,
+                                bool* aRetval)
+{
+  nsresult rv;
+
+  RefPtr<DOMStorage> storage = static_cast<DOMStorage*>(aStorage);
+  if (!storage) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  *aRetval = false;
+
+  if (!aPrincipal) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  nsAutoCString suffix;
+  BasePrincipal::Cast(aPrincipal)->OriginAttributesRef().CreateSuffix(suffix);
+
+  nsAutoCString origin;
+  rv = AppendOriginNoSuffix(aPrincipal, origin);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  DOMStorageCache* cache = GetCache(suffix, origin);
+  if (cache != storage->GetCache()) {
+    return NS_OK;
+  }
+
+  if (!storage->PrincipalEquals(aPrincipal)) {
+    return NS_OK;
+  }
+
+  *aRetval = true;
+  return NS_OK;
+}
+
+// Obsolete nsIDOMStorageManager methods
+
+NS_IMETHODIMP
+DOMStorageManager::GetLocalStorageForPrincipal(nsIPrincipal* aPrincipal,
+                                               const nsAString& aDocumentURI,
+                                               bool aPrivate,
+                                               nsIDOMStorage** aRetval)
+{
+  if (mType != LocalStorage) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  return CreateStorage(nullptr, aPrincipal, aDocumentURI, aPrivate, aRetval);
+}
+
+void
+DOMStorageManager::ClearCaches(uint32_t aUnloadFlags,
+                               const OriginAttributesPattern& aPattern,
+                               const nsACString& aOriginScope)
+{
+  for (auto iter1 = mCaches.Iter(); !iter1.Done(); iter1.Next()) {
+    PrincipalOriginAttributes oa;
+    DebugOnly<bool> rv = oa.PopulateFromSuffix(iter1.Key());
+    MOZ_ASSERT(rv);
+    if (!aPattern.Matches(oa)) {
+      // This table doesn't match the given origin attributes pattern
+      continue;
+    }
+
+    CacheOriginHashtable* table = iter1.Data();
+
+    for (auto iter2 = table->Iter(); !iter2.Done(); iter2.Next()) {
+      DOMStorageCache* cache = iter2.Get()->cache();
+
+      if (aOriginScope.IsEmpty() ||
+          StringBeginsWith(cache->OriginNoSuffix(), aOriginScope)) {
+        cache->UnloadItems(aUnloadFlags);
+      }
+    }
+  }
+}
+
+nsresult
+DOMStorageManager::Observe(const char* aTopic,
+                           const nsAString& aOriginAttributesPattern,
+                           const nsACString& aOriginScope)
+{
+  OriginAttributesPattern pattern;
+  if (!pattern.Init(aOriginAttributesPattern)) {
+    NS_ERROR("Cannot parse origin attributes pattern");
+    return NS_ERROR_FAILURE;
+  }
+
+  // Clear everything, caches + database
+  if (!strcmp(aTopic, "cookie-cleared") ||
+      !strcmp(aTopic, "extension:purge-localStorage-caches")) {
+    ClearCaches(DOMStorageCache::kUnloadComplete, pattern, EmptyCString());
+    return NS_OK;
+  }
+
+  // Clear from caches everything that has been stored
+  // while in session-only mode
+  if (!strcmp(aTopic, "session-only-cleared")) {
+    ClearCaches(DOMStorageCache::kUnloadSession, pattern, aOriginScope);
+    return NS_OK;
+  }
+
+  // Clear everything (including so and pb data) from caches and database
+  // for the gived domain and subdomains.
+  if (!strcmp(aTopic, "domain-data-cleared")) {
+    ClearCaches(DOMStorageCache::kUnloadComplete, pattern, aOriginScope);
+    return NS_OK;
+  }
+
+  // Clear all private-browsing caches
+  if (!strcmp(aTopic, "private-browsing-data-cleared")) {
+    ClearCaches(DOMStorageCache::kUnloadPrivate, pattern, EmptyCString());
+    return NS_OK;
+  }
+
+  // Clear localStorage data beloging to an origin pattern
+  if (!strcmp(aTopic, "origin-attr-pattern-cleared")) {
+    // sessionStorage is expected to stay
+    if (mType == SessionStorage) {
+      return NS_OK;
+    }
+
+    ClearCaches(DOMStorageCache::kUnloadComplete, pattern, EmptyCString());
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "profile-change")) {
+    // For case caches are still referenced - clear them completely
+    ClearCaches(DOMStorageCache::kUnloadComplete, pattern, EmptyCString());
+    mCaches.Clear();
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "low-disk-space")) {
+    if (mType == LocalStorage) {
+      mLowDiskSpace = true;
+    }
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "no-low-disk-space")) {
+    if (mType == LocalStorage) {
+      mLowDiskSpace = false;
+    }
+
+    return NS_OK;
+  }
+
+#ifdef DOM_STORAGE_TESTS
+  if (!strcmp(aTopic, "test-reload")) {
+    if (mType != LocalStorage) {
+      return NS_OK;
+    }
+
+    // This immediately completely reloads all caches from the database.
+    ClearCaches(DOMStorageCache::kTestReload, pattern, EmptyCString());
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "test-flushed")) {
+    if (!XRE_IsParentProcess()) {
+      nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+      if (obs) {
+        obs->NotifyObservers(nullptr, "domstorage-test-flushed", nullptr);
+      }
+    }
+
+    return NS_OK;
+  }
+#endif
+
+  NS_ERROR("Unexpected topic");
+  return NS_ERROR_UNEXPECTED;
+}
+
+// DOMLocalStorageManager
+
+DOMLocalStorageManager::DOMLocalStorageManager()
+  : DOMStorageManager(LocalStorage)
+{
+  NS_ASSERTION(!sSelf, "Somebody is trying to do_CreateInstance(\"@mozilla/dom/localStorage-manager;1\"");
+  sSelf = this;
+
+  if (!XRE_IsParentProcess()) {
+    // Do this only on the child process.  The thread IPC bridge
+    // is also used to communicate chrome observer notifications.
+    // Note: must be called after we set sSelf
+    DOMStorageCache::StartDatabase();
+  }
+}
+
+DOMLocalStorageManager::~DOMLocalStorageManager()
+{
+  sSelf = nullptr;
+}
+
+DOMLocalStorageManager*
+DOMLocalStorageManager::Ensure()
+{
+  if (sSelf) {
+    return sSelf;
+  }
+
+  // Cause sSelf to be populated.
+  nsCOMPtr<nsIDOMStorageManager> initializer =
+    do_GetService("@mozilla.org/dom/localStorage-manager;1");
+  MOZ_ASSERT(sSelf, "Didn't initialize?");
+
+  return sSelf;
+}
+
+// DOMSessionStorageManager
+
+DOMSessionStorageManager::DOMSessionStorageManager()
+  : DOMStorageManager(SessionStorage)
+{
+  if (!XRE_IsParentProcess()) {
+    // Do this only on the child process.  The thread IPC bridge
+    // is also used to communicate chrome observer notifications.
+    DOMStorageCache::StartDatabase();
+  }
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/DOMStorageManager.h b/dom/storage/DOMStorageManager.h
new file mode 100644
index 0000000000..666e16a6fc
--- /dev/null
+++ b/dom/storage/DOMStorageManager.h
@@ -0,0 +1,155 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 nsDOMStorageManager_h__
+#define nsDOMStorageManager_h__
+
+#include "nsIDOMStorageManager.h"
+#include "DOMStorageObserver.h"
+
+#include "DOMStorageCache.h"
+#include "mozilla/dom/DOMStorage.h"
+
+#include "nsTHashtable.h"
+#include "nsDataHashtable.h"
+#include "nsClassHashtable.h"
+#include "nsHashKeys.h"
+
+namespace mozilla {
+
+class OriginAttributesPattern;
+
+namespace dom {
+
+const DOMStorage::StorageType SessionStorage = DOMStorage::SessionStorage;
+const DOMStorage::StorageType LocalStorage = DOMStorage::LocalStorage;
+
+class DOMStorageManager : public nsIDOMStorageManager
+                        , public DOMStorageObserverSink
+{
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIDOMSTORAGEMANAGER
+
+public:
+  virtual DOMStorage::StorageType Type() { return mType; }
+
+  // Reads the preference for DOM storage quota
+  static uint32_t GetQuota();
+  // Gets (but not ensures) cache for the given scope
+  DOMStorageCache* GetCache(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix);
+  // Returns object keeping usage cache for the scope.
+  already_AddRefed<DOMStorageUsage> GetOriginUsage(const nsACString& aOriginNoSuffix);
+
+  static nsCString CreateOrigin(const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix);
+
+protected:
+  explicit DOMStorageManager(DOMStorage::StorageType aType);
+  virtual ~DOMStorageManager();
+
+private:
+  // DOMStorageObserverSink, handler to various chrome clearing notification
+  virtual nsresult Observe(const char* aTopic,
+                           const nsAString& aOriginAttributesPattern,
+                           const nsACString& aOriginScope) override;
+
+  // Since nsTHashtable doesn't like multiple inheritance, we have to aggregate
+  // DOMStorageCache into the entry.
+  class DOMStorageCacheHashKey : public nsCStringHashKey
+  {
+  public:
+    explicit DOMStorageCacheHashKey(const nsACString* aKey)
+      : nsCStringHashKey(aKey)
+      , mCache(new DOMStorageCache(aKey))
+    {}
+
+    DOMStorageCacheHashKey(const DOMStorageCacheHashKey& aOther)
+      : nsCStringHashKey(aOther)
+    {
+      NS_ERROR("Shouldn't be called");
+    }
+
+    DOMStorageCache* cache() { return mCache; }
+    // Keep the cache referenced forever, used for sessionStorage.
+    void HardRef() { mCacheRef = mCache; }
+
+  private:
+    // weak ref only since cache references its manager.
+    DOMStorageCache* mCache;
+    // hard ref when this is sessionStorage to keep it alive forever.
+    RefPtr<DOMStorageCache> mCacheRef;
+  };
+
+  // Ensures cache for a scope, when it doesn't exist it is created and initalized,
+  // this also starts preload of persistent data.
+  already_AddRefed<DOMStorageCache> PutCache(const nsACString& aOriginSuffix,
+                                             const nsACString& aOriginNoSuffix,
+                                             nsIPrincipal* aPrincipal);
+
+  // Helper for creation of DOM storage objects
+  nsresult GetStorageInternal(bool aCreate,
+                              mozIDOMWindow* aWindow,
+                              nsIPrincipal* aPrincipal,
+                              const nsAString& aDocumentURI,
+                              bool aPrivate,
+                              nsIDOMStorage** aRetval);
+
+  // Suffix->origin->cache map
+  typedef nsTHashtable<DOMStorageCacheHashKey> CacheOriginHashtable;
+  nsClassHashtable<nsCStringHashKey, CacheOriginHashtable> mCaches;
+
+  const DOMStorage::StorageType mType;
+
+  // If mLowDiskSpace is true it indicates a low device storage situation and
+  // so no localStorage writes are allowed. sessionStorage writes are still
+  // allowed.
+  bool mLowDiskSpace;
+  bool IsLowDiskSpace() const { return mLowDiskSpace; };
+
+  void ClearCaches(uint32_t aUnloadFlags,
+                   const OriginAttributesPattern& aPattern,
+                   const nsACString& aKeyPrefix);
+
+protected:
+  // Keeps usage cache objects for eTLD+1 scopes we have touched.
+  nsDataHashtable<nsCStringHashKey, RefPtr<DOMStorageUsage> > mUsages;
+
+  friend class DOMStorageCache;
+  // Releases cache since it is no longer referrered by any DOMStorage object.
+  virtual void DropCache(DOMStorageCache* aCache);
+};
+
+// Derived classes to allow two different contract ids, one for localStorage and
+// one for sessionStorage management.  localStorage manager is used as service
+// scoped to the application while sessionStorage managers are instantiated by each
+// top doc shell in the application since sessionStorages are isolated per top level
+// browsing context.  The code may easily by shared by both.
+
+class DOMLocalStorageManager final : public DOMStorageManager
+{
+public:
+  DOMLocalStorageManager();
+  virtual ~DOMLocalStorageManager();
+
+  // Global getter of localStorage manager service
+  static DOMLocalStorageManager* Self() { return sSelf; }
+
+  // Like Self, but creates an instance if we're not yet initialized.
+  static DOMLocalStorageManager* Ensure();
+
+private:
+  static DOMLocalStorageManager* sSelf;
+};
+
+class DOMSessionStorageManager final : public DOMStorageManager
+{
+public:
+  DOMSessionStorageManager();
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif /* nsDOMStorageManager_h__ */
diff --git a/dom/storage/DOMStorageObserver.cpp b/dom/storage/DOMStorageObserver.cpp
new file mode 100644
index 0000000000..a2b3f1da84
--- /dev/null
+++ b/dom/storage/DOMStorageObserver.cpp
@@ -0,0 +1,355 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "DOMStorageObserver.h"
+
+#include "DOMStorageDBThread.h"
+#include "DOMStorageCache.h"
+
+#include "mozilla/BasePrincipal.h"
+#include "nsIObserverService.h"
+#include "nsIURI.h"
+#include "nsIURL.h"
+#include "nsIScriptSecurityManager.h"
+#include "nsIPermission.h"
+#include "nsIIDNService.h"
+#include "nsICookiePermission.h"
+
+#include "nsPrintfCString.h"
+#include "nsXULAppAPI.h"
+#include "nsEscape.h"
+#include "nsNetCID.h"
+#include "mozilla/Services.h"
+#include "nsServiceManagerUtils.h"
+
+namespace mozilla {
+namespace dom {
+
+static const char kStartupTopic[] = "sessionstore-windows-restored";
+static const uint32_t kStartupDelay = 0;
+
+NS_IMPL_ISUPPORTS(DOMStorageObserver,
+                  nsIObserver,
+                  nsISupportsWeakReference)
+
+DOMStorageObserver* DOMStorageObserver::sSelf = nullptr;
+
+extern nsresult
+CreateReversedDomain(const nsACString& aAsciiDomain, nsACString& aKey);
+
+// static
+nsresult
+DOMStorageObserver::Init()
+{
+  if (sSelf) {
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (!obs) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  sSelf = new DOMStorageObserver();
+  NS_ADDREF(sSelf);
+
+  // Chrome clear operations.
+  obs->AddObserver(sSelf, kStartupTopic, true);
+  obs->AddObserver(sSelf, "cookie-changed", true);
+  obs->AddObserver(sSelf, "perm-changed", true);
+  obs->AddObserver(sSelf, "browser:purge-domain-data", true);
+  obs->AddObserver(sSelf, "last-pb-context-exited", true);
+  obs->AddObserver(sSelf, "clear-origin-attributes-data", true);
+  obs->AddObserver(sSelf, "extension:purge-localStorage", true);
+
+  // Shutdown
+  obs->AddObserver(sSelf, "profile-after-change", true);
+  obs->AddObserver(sSelf, "profile-before-change", true);
+  obs->AddObserver(sSelf, "xpcom-shutdown", true);
+
+  // Observe low device storage notifications.
+  obs->AddObserver(sSelf, "disk-space-watcher", true);
+
+#ifdef DOM_STORAGE_TESTS
+  // Testing
+  obs->AddObserver(sSelf, "domstorage-test-flush-force", true);
+  if (XRE_IsParentProcess()) {
+    // Only to forward to child process.
+    obs->AddObserver(sSelf, "domstorage-test-flushed", true);
+  }
+
+  obs->AddObserver(sSelf, "domstorage-test-reload", true);
+#endif
+
+  return NS_OK;
+}
+
+// static
+nsresult
+DOMStorageObserver::Shutdown()
+{
+  if (!sSelf) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  NS_RELEASE(sSelf);
+  return NS_OK;
+}
+
+void
+DOMStorageObserver::AddSink(DOMStorageObserverSink* aObs)
+{
+  mSinks.AppendElement(aObs);
+}
+
+void
+DOMStorageObserver::RemoveSink(DOMStorageObserverSink* aObs)
+{
+  mSinks.RemoveElement(aObs);
+}
+
+void
+DOMStorageObserver::Notify(const char* aTopic,
+                           const nsAString& aOriginAttributesPattern,
+                           const nsACString& aOriginScope)
+{
+  for (uint32_t i = 0; i < mSinks.Length(); ++i) {
+    DOMStorageObserverSink* sink = mSinks[i];
+    sink->Observe(aTopic, aOriginAttributesPattern, aOriginScope);
+  }
+}
+
+NS_IMETHODIMP
+DOMStorageObserver::Observe(nsISupports* aSubject,
+                            const char* aTopic,
+                            const char16_t* aData)
+{
+  nsresult rv;
+
+  // Start the thread that opens the database.
+  if (!strcmp(aTopic, kStartupTopic)) {
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    obs->RemoveObserver(this, kStartupTopic);
+
+    mDBThreadStartDelayTimer = do_CreateInstance(NS_TIMER_CONTRACTID);
+    if (!mDBThreadStartDelayTimer) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    mDBThreadStartDelayTimer->Init(this, nsITimer::TYPE_ONE_SHOT, kStartupDelay);
+
+    return NS_OK;
+  }
+
+  // Timer callback used to start the database a short timer after startup
+  if (!strcmp(aTopic, NS_TIMER_CALLBACK_TOPIC)) {
+    nsCOMPtr<nsITimer> timer = do_QueryInterface(aSubject);
+    if (!timer) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    if (timer == mDBThreadStartDelayTimer) {
+      mDBThreadStartDelayTimer = nullptr;
+
+      DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+      NS_ENSURE_TRUE(db, NS_ERROR_FAILURE);
+    }
+
+    return NS_OK;
+  }
+
+  // Clear everything, caches + database
+  if (!strcmp(aTopic, "cookie-changed")) {
+    if (!NS_LITERAL_STRING("cleared").Equals(aData)) {
+      return NS_OK;
+    }
+
+    DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+    NS_ENSURE_TRUE(db, NS_ERROR_FAILURE);
+
+    db->AsyncClearAll();
+
+    Notify("cookie-cleared");
+
+    return NS_OK;
+  }
+
+  // Clear from caches everything that has been stored
+  // while in session-only mode
+  if (!strcmp(aTopic, "perm-changed")) {
+    // Check for cookie permission change
+    nsCOMPtr<nsIPermission> perm(do_QueryInterface(aSubject));
+    if (!perm) {
+      return NS_OK;
+    }
+
+    nsAutoCString type;
+    perm->GetType(type);
+    if (type != NS_LITERAL_CSTRING("cookie")) {
+      return NS_OK;
+    }
+
+    uint32_t cap = 0;
+    perm->GetCapability(&cap);
+    if (!(cap & nsICookiePermission::ACCESS_SESSION) ||
+        !NS_LITERAL_STRING("deleted").Equals(nsDependentString(aData))) {
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsIPrincipal> principal;
+    perm->GetPrincipal(getter_AddRefs(principal));
+    if (!principal) {
+      return NS_OK;
+    }
+
+    nsAutoCString originSuffix;
+    BasePrincipal::Cast(principal)->OriginAttributesRef().CreateSuffix(originSuffix);
+
+    nsCOMPtr<nsIURI> origin;
+    principal->GetURI(getter_AddRefs(origin));
+    if (!origin) {
+      return NS_OK;
+    }
+
+    nsAutoCString host;
+    origin->GetHost(host);
+    if (host.IsEmpty()) {
+      return NS_OK;
+    }
+
+    nsAutoCString originScope;
+    rv = CreateReversedDomain(host, originScope);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    Notify("session-only-cleared", NS_ConvertUTF8toUTF16(originSuffix), originScope);
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "extension:purge-localStorage")) {
+    DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+    NS_ENSURE_TRUE(db, NS_ERROR_FAILURE);
+
+    db->AsyncClearAll();
+
+    Notify("extension:purge-localStorage-caches");
+
+    return NS_OK;
+  }
+
+  // Clear everything (including so and pb data) from caches and database
+  // for the gived domain and subdomains.
+  if (!strcmp(aTopic, "browser:purge-domain-data")) {
+    // Convert the domain name to the ACE format
+    nsAutoCString aceDomain;
+    nsCOMPtr<nsIIDNService> converter = do_GetService(NS_IDNSERVICE_CONTRACTID);
+    if (converter) {
+      rv = converter->ConvertUTF8toACE(NS_ConvertUTF16toUTF8(aData), aceDomain);
+      NS_ENSURE_SUCCESS(rv, rv);
+    } else {
+      // In case the IDN service is not available, this is the best we can come up with!
+      rv = NS_EscapeURL(NS_ConvertUTF16toUTF8(aData),
+                        esc_OnlyNonASCII | esc_AlwaysCopy,
+                        aceDomain,
+                        fallible);
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+
+    nsAutoCString originScope;
+    rv = CreateReversedDomain(aceDomain, originScope);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+    NS_ENSURE_TRUE(db, NS_ERROR_FAILURE);
+
+    db->AsyncClearMatchingOrigin(originScope);
+
+    Notify("domain-data-cleared", EmptyString(), originScope);
+
+    return NS_OK;
+  }
+
+  // Clear all private-browsing caches
+  if (!strcmp(aTopic, "last-pb-context-exited")) {
+    Notify("private-browsing-data-cleared");
+
+    return NS_OK;
+  }
+
+  // Clear data of the origins whose prefixes will match the suffix.
+  if (!strcmp(aTopic, "clear-origin-attributes-data")) {
+    OriginAttributesPattern pattern;
+    if (!pattern.Init(nsDependentString(aData))) {
+      NS_ERROR("Cannot parse origin attributes pattern");
+      return NS_ERROR_FAILURE;
+    }
+
+    DOMStorageDBBridge* db = DOMStorageCache::StartDatabase();
+    NS_ENSURE_TRUE(db, NS_ERROR_FAILURE);
+
+    db->AsyncClearMatchingOriginAttributes(pattern);
+
+    Notify("origin-attr-pattern-cleared", nsDependentString(aData));
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "profile-after-change")) {
+    Notify("profile-change");
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "profile-before-change") ||
+      !strcmp(aTopic, "xpcom-shutdown")) {
+    rv = DOMStorageCache::StopDatabase();
+    if (NS_FAILED(rv)) {
+      NS_WARNING("Error while stopping DOMStorage DB background thread");
+    }
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "disk-space-watcher")) {
+    if (NS_LITERAL_STRING("full").Equals(aData)) {
+      Notify("low-disk-space");
+    } else if (NS_LITERAL_STRING("free").Equals(aData)) {
+      Notify("no-low-disk-space");
+    }
+
+    return NS_OK;
+  }
+
+#ifdef DOM_STORAGE_TESTS
+  if (!strcmp(aTopic, "domstorage-test-flush-force")) {
+    DOMStorageDBBridge* db = DOMStorageCache::GetDatabase();
+    if (db) {
+      db->AsyncFlush();
+    }
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "domstorage-test-flushed")) {
+    // Only used to propagate to IPC children
+    Notify("test-flushed");
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "domstorage-test-reload")) {
+    Notify("test-reload");
+
+    return NS_OK;
+  }
+#endif
+
+  NS_ERROR("Unexpected topic");
+  return NS_ERROR_UNEXPECTED;
+}
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/DOMStorageObserver.h b/dom/storage/DOMStorageObserver.h
new file mode 100644
index 0000000000..2efce96a31
--- /dev/null
+++ b/dom/storage/DOMStorageObserver.h
@@ -0,0 +1,67 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 nsIDOMStorageObserver_h__
+#define nsIDOMStorageObserver_h__
+
+#include "nsIObserver.h"
+#include "nsITimer.h"
+#include "nsWeakReference.h"
+#include "nsTArray.h"
+#include "nsString.h"
+
+namespace mozilla {
+namespace dom {
+
+class DOMStorageObserver;
+
+// Implementers are DOMStorageManager and DOMStorageDBParent to forward to
+// child processes.
+class DOMStorageObserverSink
+{
+public:
+  virtual ~DOMStorageObserverSink() {}
+
+private:
+  friend class DOMStorageObserver;
+  virtual nsresult Observe(const char* aTopic,
+                           const nsAString& aOriginAttributesPattern,
+                           const nsACString& aOriginScope) = 0;
+};
+
+// Statically (though layout statics) initialized observer receiving and processing
+// chrome clearing notifications, such as cookie deletion etc.
+class DOMStorageObserver : public nsIObserver
+                         , public nsSupportsWeakReference
+{
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  static nsresult Init();
+  static nsresult Shutdown();
+  static DOMStorageObserver* Self() { return sSelf; }
+
+  void AddSink(DOMStorageObserverSink* aObs);
+  void RemoveSink(DOMStorageObserverSink* aObs);
+  void Notify(const char* aTopic,
+              const nsAString& aOriginAttributesPattern = EmptyString(),
+              const nsACString& aOriginScope = EmptyCString());
+
+private:
+  virtual ~DOMStorageObserver() {}
+
+  static DOMStorageObserver* sSelf;
+
+  // Weak references
+  nsTArray<DOMStorageObserverSink*> mSinks;
+  nsCOMPtr<nsITimer> mDBThreadStartDelayTimer;
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif
diff --git a/dom/storage/PStorage.ipdl b/dom/storage/PStorage.ipdl
new file mode 100644
index 0000000000..22b85f7956
--- /dev/null
+++ b/dom/storage/PStorage.ipdl
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil; tab-width: 8 -*- */
+/* vim: set sw=4 ts=8 et tw=80 ft=cpp : */
+/* 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 protocol PContent;
+
+namespace mozilla {
+namespace dom {
+
+/* This protocol bridges async access to the database thread running on the parent process
+ * and caches running on the child process.
+ */
+nested(upto inside_cpow) sync protocol PStorage
+{
+  manager PContent;
+
+parent:
+  async __delete__();
+
+  nested(inside_cpow) sync Preload(nsCString originSuffix, nsCString originNoSuffix, uint32_t alreadyLoadedCount)
+    returns (nsString[] keys, nsString[] values, nsresult rv);
+
+  async AsyncPreload(nsCString originSuffix, nsCString originNoSuffix, bool priority);
+  async AsyncGetUsage(nsCString scope);
+  async AsyncAddItem(nsCString originSuffix, nsCString originNoSuffix, nsString key, nsString value);
+  async AsyncUpdateItem(nsCString originSuffix, nsCString originNoSuffix, nsString key, nsString value);
+  async AsyncRemoveItem(nsCString originSuffix, nsCString originNoSuffix, nsString key);
+  async AsyncClear(nsCString originSuffix, nsCString originNoSuffix);
+  async AsyncFlush();
+  
+child:
+  async Observe(nsCString topic,
+                nsString originAttributesPattern,
+                nsCString originScope);
+  async OriginsHavingData(nsCString[] origins);
+  async LoadItem(nsCString originSuffix, nsCString originNoSuffix, nsString key, nsString value);
+  async LoadDone(nsCString originSuffix, nsCString originNoSuffix, nsresult rv);
+  async LoadUsage(nsCString scope, int64_t usage);
+  async Error(nsresult rv);
+};
+
+}
+}
diff --git a/dom/storage/moz.build b/dom/storage/moz.build
new file mode 100644
index 0000000000..47c2fb85f7
--- /dev/null
+++ b/dom/storage/moz.build
@@ -0,0 +1,34 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+EXPORTS.mozilla.dom += [
+    'DOMStorage.h',
+    'DOMStorageIPC.h',
+]
+
+UNIFIED_SOURCES += [
+    'DOMStorage.cpp',
+    'DOMStorageCache.cpp',
+    'DOMStorageDBThread.cpp',
+    'DOMStorageDBUpdater.cpp',
+    'DOMStorageIPC.cpp',
+    'DOMStorageManager.cpp',
+    'DOMStorageObserver.cpp',
+]
+
+IPDL_SOURCES += [
+    'PStorage.ipdl',
+]
+
+include('/ipc/chromium/chromium-config.mozbuild')
+
+FINAL_LIBRARY = 'xul'
+LOCAL_INCLUDES += [
+    '/dom/base',
+]
+
+if CONFIG['ENABLE_TESTS']:
+    DEFINES['DOM_STORAGE_TESTS'] = True