Merge pull request %834 from g4jc/remove_contextid

Issue mcp-graveyard/UXP%756 - Remove Contextual Identity

63 files changed, 113 insertions, 1791 deletions

diff --git a/application/basilisk/app/profile/basilisk.js b/application/basilisk/app/profile/basilisk.js
index 24f1c582c..4700eac44 100644
--- a/application/basilisk/app/profile/basilisk.js
+++ b/application/basilisk/app/profile/basilisk.js
@@ -1293,17 +1293,6 @@ pref("privacy.trackingprotection.ui.enabled", true);
 pref("privacy.trackingprotection.ui.enabled", false);
 #endif
 
-// Enable Contextual Identity Containers
-#ifdef NIGHTLY_BUILD
-pref("privacy.userContext.enabled", true);
-pref("privacy.userContext.ui.enabled", true);
-pref("privacy.usercontext.about_newtab_segregation.enabled", true);
-#else
-pref("privacy.userContext.enabled", false);
-pref("privacy.userContext.ui.enabled", false);
-pref("privacy.usercontext.about_newtab_segregation.enabled", false);
-#endif
-
 #ifndef RELEASE_OR_BETA
 // At the moment, autostart.2 is used, while autostart.1 is unused.
 // We leave it here set to false to reset users' defaults and allow
diff --git a/application/basilisk/base/content/browser-context.inc b/application/basilisk/base/content/browser-context.inc
index 36e0478af..2f6b19da0 100644
--- a/application/basilisk/base/content/browser-context.inc
+++ b/application/basilisk/base/content/browser-context.inc
@@ -51,23 +51,11 @@
                 label="&openLinkCmdInCurrent.label;"
                 accesskey="&openLinkCmdInCurrent.accesskey;"
                 oncommand="gContextMenu.openLinkInCurrent();"/>
-# label and data-usercontextid are dynamically set.
-      <menuitem id="context-openlinkincontainertab"
-                accesskey="&openLinkCmdInTab.accesskey;"
-                oncommand="gContextMenu.openLinkInTab(event);"/>
+# label is dynamically set.
       <menuitem id="context-openlinkintab"
                 label="&openLinkCmdInTab.label;"
                 accesskey="&openLinkCmdInTab.accesskey;"
-                data-usercontextid="0"
-                oncommand="gContextMenu.openLinkInTab(event);"/>
-
-      <menu id="context-openlinkinusercontext-menu"
-            label="&openLinkCmdInContainerTab.label;"
-            accesskey="&openLinkCmdInContainerTab.accesskey;"
-            hidden="true">
-        <menupopup oncommand="gContextMenu.openLinkInTab(event);"
-                   onpopupshowing="return gContextMenu.createContainerMenu(event);" />
-      </menu>
+                oncommand="gContextMenu.openLinkInTab();"/>
 
       <menuitem id="context-openlink"
                 label="&openLinkCmd.label;"
diff --git a/application/basilisk/base/content/browser-menubar.inc b/application/basilisk/base/content/browser-menubar.inc
index 41734711c..0549ad915 100644
--- a/application/basilisk/base/content/browser-menubar.inc
+++ b/application/basilisk/base/content/browser-menubar.inc
@@ -11,19 +11,12 @@
                 style="border:0px;padding:0px;margin:0px;-moz-appearance:none">
             <menu id="file-menu" label="&fileMenu.label;"
                   accesskey="&fileMenu.accesskey;">
-              <menupopup id="menu_FilePopup"
-                         onpopupshowing="updateUserContextUIVisibility();">
+              <menupopup id="menu_FilePopup">
                 <menuitem id="menu_newNavigatorTab"
                           label="&tabCmd.label;"
                           command="cmd_newNavigatorTab"
                           key="key_newNavigatorTab"
                           accesskey="&tabCmd.accesskey;"/>
-                <menu id="menu_newUserContext"
-                      label="&newUserContext.label;"
-                      accesskey="&newUserContext.accesskey;"
-                      hidden="true">
-                  <menupopup onpopupshowing="return createUserContextMenu(event);" />
-                </menu>
                 <menuitem id="menu_newNavigator"
                           label="&newNavigatorCmd.label;"
                           accesskey="&newNavigatorCmd.accesskey;"
diff --git a/application/basilisk/base/content/browser.js b/application/basilisk/base/content/browser.js
index e3a5393a0..ddbe11a9d 100644
--- a/application/basilisk/base/content/browser.js
+++ b/application/basilisk/base/content/browser.js
@@ -8,7 +8,6 @@ var Cu = Components.utils;
 var Cc = Components.classes;
 
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
-Cu.import("resource://gre/modules/ContextualIdentityService.jsm");
 Cu.import("resource://gre/modules/NotificationDB.jsm");
 
 // lazy module getters
@@ -827,10 +826,6 @@ function _loadURIWithFlags(browser, uri, params) {
   }
   try {
     if (!mustChangeProcess) {
-      if (params.userContextId) {
-        browser.webNavigation.setOriginAttributesBeforeLoading({ userContextId: params.userContextId });
-      }
-
       browser.webNavigation.loadURIWithOptions(uri, flags,
                                                referrer, referrerPolicy,
                                                postData, null, null, triggeringPrincipal);
@@ -856,10 +851,6 @@ function _loadURIWithFlags(browser, uri, params) {
         postData: postData
       }
 
-      if (params.userContextId) {
-        loadParams.userContextId = params.userContextId;
-      }
-
       LoadInOtherProcess(browser, loadParams);
     }
   } catch (e) {
@@ -872,10 +863,6 @@ function _loadURIWithFlags(browser, uri, params) {
       Cu.reportError(e);
       gBrowser.updateBrowserRemotenessByURL(browser, uri);
 
-      if (params.userContextId) {
-        browser.webNavigation.setOriginAttributesBeforeLoading({ userContextId: params.userContextId });
-      }
-
       browser.webNavigation.loadURIWithOptions(uri, flags, referrer, referrerPolicy,
                                                postData, null, null, triggeringPrincipal);
     } else {
@@ -939,16 +926,6 @@ addEventListener("DOMContentLoaded", function onDCL() {
   let initBrowser =
     document.getAnonymousElementByAttribute(gBrowser, "anonid", "initialBrowser");
 
-  // The window's first argument is a tab if and only if we are swapping tabs.
-  // We must set the browser's usercontextid before updateBrowserRemoteness(),
-  // so that the newly created remote tab child has the correct usercontextid.
-  if (window.arguments) {
-    let tabToOpen = window.arguments[0];
-    if (tabToOpen instanceof XULElement && tabToOpen.hasAttribute("usercontextid")) {
-      initBrowser.setAttribute("usercontextid", tabToOpen.getAttribute("usercontextid"));
-    }
-  }
-
   gBrowser.updateBrowserRemoteness(initBrowser, gMultiProcessBrowser);
 });
 
@@ -1133,13 +1110,6 @@ var gBrowserInit = {
         // make sure it has a docshell
         gBrowser.docShell;
 
-        // We must set usercontextid before updateBrowserRemoteness()
-        // so that the newly created remote tab child has correct usercontextid
-        if (tabToOpen.hasAttribute("usercontextid")) {
-          let usercontextid = tabToOpen.getAttribute("usercontextid");
-          gBrowser.selectedBrowser.setAttribute("usercontextid", usercontextid);
-        }
-
         // If the browser that we're swapping in was remote, then we'd better
         // be able to support remote browsers, and then make our selectedTab
         // remote.
@@ -1165,9 +1135,8 @@ var gBrowserInit = {
       //                 [3]: postData (nsIInputStream)
       //                 [4]: allowThirdPartyFixup (bool)
       //                 [5]: referrerPolicy (int)
-      //                 [6]: userContextId (int)
-      //                 [7]: originPrincipal (nsIPrincipal)
-      //                 [8]: triggeringPrincipal (nsIPrincipal)
+      //                 [6]: originPrincipal (nsIPrincipal)
+      //                 [7]: triggeringPrincipal (nsIPrincipal)
       else if (window.arguments.length >= 3) {
         let referrerURI = window.arguments[2];
         if (typeof(referrerURI) == "string") {
@@ -1179,13 +1148,11 @@ var gBrowserInit = {
         }
         let referrerPolicy = (window.arguments[5] != undefined ?
             window.arguments[5] : Ci.nsIHttpChannel.REFERRER_POLICY_DEFAULT);
-        let userContextId = (window.arguments[6] != undefined ?
-            window.arguments[6] : Ci.nsIScriptSecurityManager.DEFAULT_USER_CONTEXT_ID);
         loadURI(uriToLoad, referrerURI, window.arguments[3] || null,
-                window.arguments[4] || false, referrerPolicy, userContextId,
+                window.arguments[4] || false, referrerPolicy,
                 // pass the origin principal (if any) and force its use to create
                 // an initial about:blank viewer if present:
-                window.arguments[7], !!window.arguments[7], window.arguments[8]);
+                window.arguments[6], !!window.arguments[6], window.arguments[7]);
         window.focus();
       }
       // Note: loadOneOrMoreURIs *must not* be called if window.arguments.length >= 3.
@@ -2070,7 +2037,7 @@ function BrowserTryToCloseWindow()
 }
 
 function loadURI(uri, referrer, postData, allowThirdPartyFixup, referrerPolicy,
-                 userContextId, originPrincipal, forceAboutBlankViewerInCurrent,
+                 originPrincipal, forceAboutBlankViewerInCurrent,
                  triggeringPrincipal) {
   try {
     openLinkIn(uri, "current",
@@ -2078,7 +2045,6 @@ function loadURI(uri, referrer, postData, allowThirdPartyFixup, referrerPolicy,
                  referrerPolicy: referrerPolicy,
                  postData: postData,
                  allowThirdPartyFixup: allowThirdPartyFixup,
-                 userContextId: userContextId,
                  originPrincipal,
                  triggeringPrincipal,
                  forceAboutBlankViewerInCurrent,
@@ -3951,66 +3917,6 @@ function updateEditUIVisibility()
 }
 
 /**
- * Opens a new tab with the userContextId specified as an attribute of
- * sourceEvent. This attribute is propagated to the top level originAttributes
- * living on the tab's docShell.
- *
- * @param event
- *        A click event on a userContext File Menu option
- */
-function openNewUserContextTab(event)
-{
-  openUILinkIn(BROWSER_NEW_TAB_URL, "tab", {
-    userContextId: parseInt(event.target.getAttribute('data-usercontextid')),
-  });
-}
-
-/**
- * Updates File Menu User Context UI visibility depending on
- * privacy.userContext.enabled pref state.
- */
-function updateUserContextUIVisibility()
-{
-  let menu = document.getElementById("menu_newUserContext");
-  menu.hidden = !Services.prefs.getBoolPref("privacy.userContext.enabled");
-  if (PrivateBrowsingUtils.isWindowPrivate(window)) {
-    menu.setAttribute("disabled", "true");
-  }
-}
-
-/**
- * Updates the User Context UI indicators if the browser is in a non-default context
- */
-function updateUserContextUIIndicator()
-{
-  let hbox = document.getElementById("userContext-icons");
-
-  let userContextId = gBrowser.selectedBrowser.getAttribute("usercontextid");
-  if (!userContextId) {
-    hbox.setAttribute("data-identity-color", "");
-    hbox.hidden = true;
-    return;
-  }
-
-  let identity = ContextualIdentityService.getIdentityFromId(userContextId);
-  if (!identity) {
-    hbox.setAttribute("data-identity-color", "");
-    hbox.hidden = true;
-    return;
-  }
-
-  hbox.setAttribute("data-identity-color", identity.color);
-
-  let label = document.getElementById("userContext-label");
-  label.setAttribute("value", ContextualIdentityService.getUserContextLabel(userContextId));
-
-  let indicator = document.getElementById("userContext-indicator");
-  indicator.setAttribute("data-identity-icon", identity.icon);
-
-  hbox.hidden = false;
-}
-
-/**
  * Makes the Character Encoding menu enabled or disabled as appropriate.
  * To be called when the View menu or the app menu is opened.
  */
@@ -4690,7 +4596,6 @@ nsBrowserAccess.prototype = {
 
   _openURIInNewTab: function(aURI, aReferrer, aReferrerPolicy, aIsPrivate,
                              aIsExternal, aForceNotRemote=false,
-                             aUserContextId=Ci.nsIScriptSecurityManager.DEFAULT_USER_CONTEXT_ID,
                              aOpener = null, aTriggeringPrincipal = null) {
     let win, needToFocusWin;
 
@@ -4719,7 +4624,6 @@ nsBrowserAccess.prototype = {
                                       triggeringPrincipal: aTriggeringPrincipal,
                                       referrerURI: aReferrer,
                                       referrerPolicy: aReferrerPolicy,
-                                      userContextId: aUserContextId,
                                       fromExternal: aIsExternal,
                                       inBackground: loadInBackground,
                                       forceNotRemote: aForceNotRemote,
@@ -4796,13 +4700,10 @@ nsBrowserAccess.prototype = {
         // will do the job of shuttling off the newly opened browser to run in
         // the right process once it starts loading a URI.
         let forceNotRemote = !!aOpener;
-        let userContextId = aOpener && aOpener.document
-                              ? aOpener.document.nodePrincipal.originAttributes.userContextId
-                              : Ci.nsIScriptSecurityManager.DEFAULT_USER_CONTEXT_ID;
         let openerWindow = (aFlags & Ci.nsIBrowserDOMWindow.OPEN_NO_OPENER) ? null : aOpener;
         let browser = this._openURIInNewTab(aURI, referrer, referrerPolicy,
                                             isPrivate, isExternal,
-                                            forceNotRemote, userContextId,
+                                            forceNotRemote,
                                             openerWindow, triggeringPrincipal);
         if (browser)
           newWindow = browser.contentWindow;
@@ -4834,16 +4735,10 @@ nsBrowserAccess.prototype = {
 
     var isExternal = !!(aFlags & Ci.nsIBrowserDOMWindow.OPEN_EXTERNAL);
 
-    var userContextId = aParams.openerOriginAttributes &&
-                        ("userContextId" in aParams.openerOriginAttributes)
-                          ? aParams.openerOriginAttributes.userContextId
-                          : Ci.nsIScriptSecurityManager.DEFAULT_USER_CONTEXT_ID
-
     let browser = this._openURIInNewTab(aURI, aParams.referrer,
                                         aParams.referrerPolicy,
                                         aParams.isPrivate,
                                         isExternal, false,
-                                        userContextId, null,
                                         aParams.triggeringPrincipal);
     if (browser)
       return browser.QueryInterface(Ci.nsIFrameLoaderOwner);
@@ -5400,11 +5295,6 @@ function handleLinkClick(event, href, linkNode) {
     triggeringPrincipal: doc.nodePrincipal,
   };
 
-  // The new tab/window must use the same userContextId
-  if (doc.nodePrincipal.originAttributes.userContextId) {
-    params.userContextId = doc.nodePrincipal.originAttributes.userContextId;
-  }
-
   openLinkIn(href, where, params);
   event.preventDefault();
   return true;
@@ -5476,8 +5366,6 @@ function handleDroppedLink(event, urlOrLinks, name)
 
   let lastLocationChange = gBrowser.selectedBrowser.lastLocationChange;
 
-  let userContextId = gBrowser.selectedBrowser.getAttribute("usercontextid");
-
   // event is null if links are dropped in content process.
   // inBackground should be false, as it's loading into current browser.
   let inBackground = false;
@@ -5501,7 +5389,6 @@ function handleDroppedLink(event, urlOrLinks, name)
         replace: true,
         allowThirdPartyFixup: false,
         postDatas,
-        userContextId,
       });
     }
   });
diff --git a/application/basilisk/base/content/browser.xul b/application/basilisk/base/content/browser.xul
index be64f1bac..0cc4c982a 100644
--- a/application/basilisk/base/content/browser.xul
+++ b/application/basilisk/base/content/browser.xul
@@ -8,7 +8,6 @@
 
 <?xml-stylesheet href="chrome://browser/content/browser.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/content/places/places.css" type="text/css"?>
-<?xml-stylesheet href="chrome://browser/content/usercontext/usercontext.css" type="text/css"?>
 #ifdef MOZ_DEVTOOLS
 <?xml-stylesheet href="chrome://devtools/skin/devtools-browser.css" type="text/css"?>
 #endif
@@ -551,12 +550,7 @@
                     key="key_undoCloseTab"
                     label="&undoCloseTab.label;"
                     observes="History:UndoCloseTab"/>
-          <menuseparator id="alltabs-popup-separator-1"/>
-          <menu id="alltabs_containersTab"
-                label="&newUserContext.label;">
-            <menupopup id="alltabs_containersMenuTab" />
-          </menu>
-          <menuseparator id="alltabs-popup-separator-2"/>
+          <menuseparator id="alltabs-popup-separator"/>
         </menupopup>
       </toolbarbutton>
 
diff --git a/application/basilisk/base/content/content.js b/application/basilisk/base/content/content.js
index 5accbdf7b..d2a70ba11 100644
--- a/application/basilisk/base/content/content.js
+++ b/application/basilisk/base/content/content.js
@@ -162,9 +162,6 @@ var handleContentContextMenu = function (event) {
 
   let selectionInfo = BrowserUtils.getSelectionDetails(content);
 
-  let loadContext = docShell.QueryInterface(Ci.nsILoadContext);
-  let userContextId = loadContext.originAttributes.userContextId;
-
   if (Services.appinfo.processType == Services.appinfo.PROCESS_TYPE_CONTENT) {
     let editFlags = SpellCheckHelper.isEditable(event.target, content);
     let spellInfo;
@@ -188,7 +185,7 @@ var handleContentContextMenu = function (event) {
                      principal, docLocation, charSet, baseURI, referrer,
                      referrerPolicy, contentType, contentDisposition,
                      frameOuterWindowID, selectionInfo, disableSetDesktopBg,
-                     loginFillInfo, parentAllowsMixedContent, userContextId },
+                     loginFillInfo, parentAllowsMixedContent },
                    { event, popupNode: event.target });
   }
   else {
@@ -212,7 +209,6 @@ var handleContentContextMenu = function (event) {
       disableSetDesktopBackground: disableSetDesktopBg,
       loginFillInfo,
       parentAllowsMixedContent,
-      userContextId,
     };
   }
 }
diff --git a/application/basilisk/base/content/nsContextMenu.js b/application/basilisk/base/content/nsContextMenu.js
index 3f77dcb90..74a2e7a8e 100644
--- a/application/basilisk/base/content/nsContextMenu.js
+++ b/application/basilisk/base/content/nsContextMenu.js
@@ -4,7 +4,6 @@
 # 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/.
 
-Components.utils.import("resource://gre/modules/ContextualIdentityService.jsm");
 Components.utils.import("resource://gre/modules/PrivateBrowsingUtils.jsm");
 Components.utils.import("resource://gre/modules/InlineSpellChecker.jsm");
 Components.utils.import("resource://gre/modules/LoginManagerContextMenu.jsm");
@@ -142,28 +141,11 @@ nsContextMenu.prototype = {
       this.onPlainTextLink = true;
     }
 
-    var inContainer = false;
-    if (gContextMenuContentData.userContextId) {
-      inContainer = true;
-      var item = document.getElementById("context-openlinkincontainertab");
-
-      item.setAttribute("data-usercontextid", gContextMenuContentData.userContextId);
-
-      var label =
-        ContextualIdentityService.getUserContextLabel(gContextMenuContentData.userContextId);
-      item.setAttribute("label",
-         gBrowserBundle.formatStringFromName("userContextOpenLink.label",
-                                             [label], 1));
-    }
-
     var shouldShow = this.onSaveableLink || isMailtoInternal || this.onPlainTextLink;
     var isWindowPrivate = PrivateBrowsingUtils.isWindowPrivate(window);
-    var showContainers = Services.prefs.getBoolPref("privacy.userContext.enabled");
     this.showItem("context-openlink", shouldShow && !isWindowPrivate);
     this.showItem("context-openlinkprivate", shouldShow);
-    this.showItem("context-openlinkintab", shouldShow && !inContainer);
-    this.showItem("context-openlinkincontainertab", shouldShow && inContainer);
-    this.showItem("context-openlinkinusercontext-menu", shouldShow && !isWindowPrivate && showContainers);
+    this.showItem("context-openlinkintab", shouldShow);
     this.showItem("context-openlinkincurrent", this.onPlainTextLink);
     this.showItem("context-sep-open", shouldShow);
   },
@@ -958,13 +940,6 @@ nsContextMenu.prototype = {
       params[p] = extra[p];
     }
 
-    // If we want to change userContextId, we must be sure that we don't
-    // propagate the referrer.
-    if ("userContextId" in params &&
-        params.userContextId != gContextMenuContentData.userContextId) {
-      params.noReferrer = true;
-    }
-
     return params;
   },
 
@@ -982,7 +957,7 @@ nsContextMenu.prototype = {
   },
 
   // Open linked-to URL in a new tab.
-  openLinkInTab: function(event) {
+  openLinkInTab: function() {
     urlSecurityCheck(this.linkURL, this.principal);
     let referrerURI = gContextMenuContentData.documentURIObject;
 
@@ -1003,7 +978,6 @@ nsContextMenu.prototype = {
 
     let params = {
       allowMixedContent: persistAllowMixedContentInChildTab,
-      userContextId: parseInt(event.target.getAttribute('data-usercontextid')),
     };
 
     openLinkIn(this.linkURL, "tab", this._openLinkInParameters(params));
@@ -1779,8 +1753,4 @@ nsContextMenu.prototype = {
     menuItem.label = menuLabel;
     menuItem.accessKey = gNavigatorBundle.getString("contextMenuSearch.accesskey");
   },
-  createContainerMenu: function(aEvent) {
-    return createUserContextMenu(aEvent, true,
-                                 gContextMenuContentData.userContextId);
-  },
 };
diff --git a/application/basilisk/base/content/tab-content.js b/application/basilisk/base/content/tab-content.js
index 7441b2140..35ef8ceb2 100644
--- a/application/basilisk/base/content/tab-content.js
+++ b/application/basilisk/base/content/tab-content.js
@@ -886,33 +886,6 @@ var RefreshBlocker = {
 
 RefreshBlocker.init();
 
-var UserContextIdNotifier = {
-  init() {
-    addEventListener("DOMWindowCreated", this);
-  },
-
-  uninit() {
-    removeEventListener("DOMWindowCreated", this);
-  },
-
-  handleEvent(aEvent) {
-    // When the window is created, we want to inform the tabbrowser about
-    // the userContextId in use in order to update the UI correctly.
-    // Just because we cannot change the userContextId from an active docShell,
-    // we don't need to check DOMContentLoaded again.
-    this.uninit();
-
-    // We use the docShell because content.document can have been loaded before
-    // setting the originAttributes.
-    let loadContext = docShell.QueryInterface(Ci.nsILoadContext);
-    let userContextId = loadContext.originAttributes.userContextId;
-
-    sendAsyncMessage("Browser:WindowCreated", { userContextId });
-  }
-};
-
-UserContextIdNotifier.init();
-
 addMessageListener("AllowScriptsToClose", () => {
   content.QueryInterface(Ci.nsIInterfaceRequestor)
          .getInterface(Ci.nsIDOMWindowUtils)
diff --git a/application/basilisk/base/content/tabbrowser.xml b/application/basilisk/base/content/tabbrowser.xml
index 52c51db69..c2f02512d 100644
--- a/application/basilisk/base/content/tabbrowser.xml
+++ b/application/basilisk/base/content/tabbrowser.xml
@@ -814,10 +814,8 @@
                 }
 
                 let unifiedComplete = this.mTabBrowser._unifiedComplete;
-                let userContextId = this.mBrowser.getAttribute("usercontextid") || 0;
                 if (this.mBrowser.registeredOpenURI) {
-                  unifiedComplete.unregisterOpenPage(this.mBrowser.registeredOpenURI,
-                                                     userContextId);
+                  unifiedComplete.unregisterOpenPage(this.mBrowser.registeredOpenURI);
                   delete this.mBrowser.registeredOpenURI;
                 }
                 // Tabs in private windows aren't registered as "Open" so
@@ -825,7 +823,7 @@
                 if (!isBlankPageURL(aLocation.spec) &&
                     (!PrivateBrowsingUtils.isWindowPrivate(window) ||
                     PrivateBrowsingUtils.permanentPrivateBrowsing)) {
-                  unifiedComplete.registerOpenPage(aLocation, userContextId);
+                  unifiedComplete.registerOpenPage(aLocation);
                   this.mBrowser.registeredOpenURI = aLocation;
                 }
               }
@@ -1230,7 +1228,6 @@
                 this._adjustFocusAfterTabSwitch(this.mCurrentTab);
             }
 
-            updateUserContextUIIndicator();
             gIdentityHandler.updateSharingIndicator();
 
             this.tabContainer._setPositionalAttributes();
@@ -1486,7 +1483,6 @@
             var aSkipAnimation;
             var aForceNotRemote;
             var aNoReferrer;
-            var aUserContextId;
             var aRelatedBrowser;
             var aOriginPrincipal;
             var aOpener;
@@ -1507,7 +1503,6 @@
               aSkipAnimation        = params.skipAnimation;
               aForceNotRemote       = params.forceNotRemote;
               aNoReferrer           = params.noReferrer;
-              aUserContextId        = params.userContextId;
               aRelatedBrowser       = params.relatedBrowser;
               aOriginPrincipal      = params.originPrincipal;
               aOpener               = params.opener;
@@ -1530,7 +1525,6 @@
                                   allowMixedContent: aAllowMixedContent,
                                   forceNotRemote: aForceNotRemote,
                                   noReferrer: aNoReferrer,
-                                  userContextId: aUserContextId,
                                   originPrincipal: aOriginPrincipal,
                                   relatedBrowser: aRelatedBrowser,
                                   opener: aOpener });
@@ -1551,7 +1545,6 @@
           let aTargetTab;
           let aNewIndex = -1;
           let aPostDatas = [];
-          let aUserContextId;
           if (arguments.length == 2 &&
               typeof arguments[1] == "object") {
             let params = arguments[1];
@@ -1562,7 +1555,6 @@
             aNewIndex             = typeof params.newIndex === "number" ?
                                     params.newIndex : aNewIndex;
             aPostDatas            = params.postDatas || aPostDatas;
-            aUserContextId        = params.userContextId;
           }
 
           if (!aURIs.length)
@@ -1611,8 +1603,7 @@
               ownerTab: owner,
               skipAnimation: multiple,
               allowThirdPartyFixup: aAllowThirdPartyFixup,
-              postData: aPostDatas[0],
-              userContextId: aUserContextId
+              postData: aPostDatas[0]
             });
             if (aNewIndex !== -1) {
               this.moveTabTo(firstTabAdded, aNewIndex);
@@ -1625,8 +1616,7 @@
             let tab = this.addTab(aURIs[i], {
               skipAnimation: true,
               allowThirdPartyFixup: aAllowThirdPartyFixup,
-              postData: aPostDatas[i],
-              userContextId: aUserContextId
+              postData: aPostDatas[i]
             });
             if (targetTabIndex !== -1)
               this.moveTabTo(tab, ++tabNum);
@@ -1899,7 +1889,7 @@
         <body>
           <![CDATA[
             // Supported parameters:
-            // userContextId, remote, isPreloadBrowser, uriIsAboutBlank, permanentKey
+            // remote, isPreloadBrowser, uriIsAboutBlank, permanentKey
 
             const NS_XUL = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
 
@@ -1911,10 +1901,6 @@
             b.setAttribute("contextmenu", this.getAttribute("contentcontextmenu"));
             b.setAttribute("tooltip", this.getAttribute("contenttooltip"));
 
-            if (aParams.userContextId) {
-              b.setAttribute("usercontextid", aParams.userContextId);
-            }
-
             if (aParams.remote) {
               b.setAttribute("remote", "true");
             }
@@ -1993,7 +1979,7 @@
             "use strict";
 
             // Supported parameters:
-            // forceNotRemote, userContextId
+            // forceNotRemote
 
             let uriIsAboutBlank = !aURI || aURI == "about:blank";
 
@@ -2011,7 +1997,6 @@
             // Private windows are not included because both the label and the
             // icon for the tab would be set incorrectly (see bug 1195981).
             if (aURI == BROWSER_NEW_TAB_URL &&
-                !aParams.userContextId &&
                 !PrivateBrowsingUtils.isWindowPrivate(window)) {
               browser = this._getPreloadedBrowser();
               if (browser) {
@@ -2025,7 +2010,6 @@
               browser = this._createBrowser({permanentKey: aTab.permanentKey,
                                              remote: remote,
                                              uriIsAboutBlank: uriIsAboutBlank,
-                                             userContextId: aParams.userContextId,
                                              relatedBrowser: aParams.relatedBrowser,
                                              opener: aParams.opener});
             }
@@ -2100,7 +2084,6 @@
             var aAllowMixedContent;
             var aForceNotRemote;
             var aNoReferrer;
-            var aUserContextId;
             var aEventDetail;
             var aRelatedBrowser;
             var aOriginPrincipal;
@@ -2123,7 +2106,6 @@
               aAllowMixedContent    = params.allowMixedContent;
               aForceNotRemote       = params.forceNotRemote;
               aNoReferrer           = params.noReferrer;
-              aUserContextId        = params.userContextId;
               aEventDetail          = params.eventDetail;
               aRelatedBrowser       = params.relatedBrowser;
               aOriginPrincipal      = params.originPrincipal;
@@ -2150,11 +2132,6 @@
               t.setAttribute("label", aURI);
             }
 
-            if (aUserContextId) {
-              t.setAttribute("usercontextid", aUserContextId);
-              ContextualIdentityService.setTabStyle(t);
-            }
-
             t.setAttribute("crop", "end");
             t.setAttribute("onerror", "this.removeAttribute('image');");
 
@@ -2204,7 +2181,6 @@
             // of tab.linkedBrowser.
             let browserParams = {
               forceNotRemote: aForceNotRemote,
-              userContextId:  aUserContextId,
               relatedBrowser: aRelatedBrowser,
               opener: aOpener,
             };
@@ -2583,8 +2559,7 @@
             listener.destroy();
 
             if (browser.registeredOpenURI && !aAdoptedByTab) {
-              this._unifiedComplete.unregisterOpenPage(browser.registeredOpenURI,
-                                                       browser.getAttribute("usercontextid") || 0);
+              this._unifiedComplete.unregisterOpenPage(browser.registeredOpenURI);
               delete browser.registeredOpenURI;
             }
 
@@ -2783,11 +2758,6 @@
             if (ourBrowser.isRemoteBrowser != otherBrowser.isRemoteBrowser)
               return;
 
-            // Keep the userContextId if set on other browser
-            if (otherBrowser.hasAttribute("usercontextid")) {
-              ourBrowser.setAttribute("usercontextid", otherBrowser.getAttribute("usercontextid"));
-            }
-
             // That's gBrowser for the other window, not the tab's browser!
             var remoteBrowser = aOtherTab.ownerDocument.defaultView.gBrowser;
             var isPending = aOtherTab.hasAttribute("pending");
@@ -2820,10 +2790,6 @@
               aOurTab.setAttribute("soundplaying", "true");
               modifiedAttrs.push("soundplaying");
             }
-            if (aOtherTab.hasAttribute("usercontextid")) {
-              aOurTab.setUserContextId(aOtherTab.getAttribute("usercontextid"));
-              modifiedAttrs.push("usercontextid");
-            }
             if (aOtherTab.hasAttribute("sharing")) {
               aOurTab.setAttribute("sharing", aOtherTab.getAttribute("sharing"));
               modifiedAttrs.push("sharing");
@@ -2961,8 +2927,7 @@
           <![CDATA[
             // If the current URI is registered as open remove it from the list.
             if (aOurBrowser.registeredOpenURI) {
-              this._unifiedComplete.unregisterOpenPage(aOurBrowser.registeredOpenURI,
-                                                       aOurBrowser.getAttribute("usercontextid") || 0);
+              this._unifiedComplete.unregisterOpenPage(aOurBrowser.registeredOpenURI);
               delete aOurBrowser.registeredOpenURI;
             }
 
@@ -3302,10 +3267,6 @@
           // it in the other window (making it seem to have moved between
           // windows).
           let params = { eventDetail: { adoptedTab: aTab } };
-          if (aTab.hasAttribute("usercontextid")) {
-            // new tab must have the same usercontextid as the old one
-            params.userContextId = aTab.getAttribute("usercontextid");
-          }
           let newTab = this.addTab("about:blank", params);
           let newBrowser = this.getBrowserForTab(newTab);
           let newURL = aTab.linkedBrowser.currentURI.spec;
@@ -4625,7 +4586,6 @@
                                           disableSetDesktopBackground: data.disableSetDesktopBg,
                                           loginFillInfo: data.loginFillInfo,
                                           parentAllowsMixedContent: data.parentAllowsMixedContent,
-                                          userContextId: data.userContextId,
                                         };
               let popup = browser.ownerDocument.getElementById("contentAreaContextMenu");
               let event = gContextMenuContentData.event;
@@ -4652,17 +4612,6 @@
             }
             case "Browser:WindowCreated": {
               let tab = this.getTabForBrowser(browser);
-              if (tab && data.userContextId) {
-                ContextualIdentityService.telemetry(data.userContextId);
-                tab.setUserContextId(data.userContextId);
-              }
-
-	      // We don't want to update the container icon and identifier if
-	      // this is not the selected browser.
-              if (browser == gBrowser.selectedBrowser) {
-                updateUserContextUIIndicator();
-              }
-
               break;
             }
             case "Findbar:Keypress": {
@@ -4845,8 +4794,7 @@
           for (let tab of this.tabs) {
             let browser = tab.linkedBrowser;
             if (browser.registeredOpenURI) {
-              this._unifiedComplete.unregisterOpenPage(browser.registeredOpenURI,
-                                                       browser.getAttribute("usercontextid") || 0);
+              this._unifiedComplete.unregisterOpenPage(browser.registeredOpenURI);
               delete browser.registeredOpenURI;
             }
             let filter = this._tabFilters.get(tab);
@@ -5247,7 +5195,7 @@
       </xul:arrowscrollbox>
     </content>
 
-    <implementation implements="nsIDOMEventListener, nsIObserver">
+    <implementation implements="nsIDOMEventListener">
       <constructor>
         <![CDATA[
           this.mTabClipWidth = Services.prefs.getIntPref("browser.tabs.tabClipWidth");
@@ -5266,17 +5214,9 @@
             this._tabAnimationLoggingEnabled = false;
           }
           this._browserNewtabpageEnabled = Services.prefs.getBoolPref("browser.newtabpage.enabled");
-          this.observe(null, "nsPref:changed", "privacy.userContext.enabled");
-          Services.prefs.addObserver("privacy.userContext.enabled", this, false);
         ]]>
       </constructor>
 
-      <destructor>
-        <![CDATA[
-          Services.prefs.removeObserver("privacy.userContext.enabled", this);
-        ]]>
-      </destructor>
-
       <field name="tabbrowser" readonly="true">
         document.getElementById(this.getAttribute("tabbrowser"));
       </field>
@@ -5302,55 +5242,6 @@
       <field name="_afterHoveredTab">null</field>
       <field name="_hoveredTab">null</field>
 
-      <method name="observe">
-        <parameter name="aSubject"/>
-        <parameter name="aTopic"/>
-        <parameter name="aData"/>
-        <body><![CDATA[
-          switch (aTopic) {
-            case "nsPref:changed":
-              // This is the only pref observed.
-              let containersEnabled = Services.prefs.getBoolPref("privacy.userContext.enabled");
-
-              const newTab = document.getElementById("new-tab-button");
-              const newTab2 = document.getAnonymousElementByAttribute(this, "anonid", "tabs-newtab-button")
-
-              if (containersEnabled) {
-                for (let parent of [newTab, newTab2]) {
-                  if (!parent)
-                    continue;
-                  let popup = document.createElementNS(
-                                "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul",
-                                "menupopup");
-                  if (parent.id) {
-                    popup.id = "newtab-popup";
-                  } else {
-                    popup.setAttribute("anonid", "newtab-popup");
-                  }
-                  popup.className = "new-tab-popup";
-                  popup.setAttribute("position", "after_end");
-                  parent.appendChild(popup);
-
-                  gClickAndHoldListenersOnElement.add(parent);
-                  parent.setAttribute("type", "menu");
-                }
-              } else {
-                for (let parent of [newTab, newTab2]) {
-                  if (!parent)
-                    continue;
-                  gClickAndHoldListenersOnElement.remove(parent);
-                  parent.removeAttribute("type");
-                  if (!parent.firstChild)
-                    continue;
-                  parent.firstChild.remove();
-                }
-              }
-
-              break;
-          }
-        ]]></body>
-      </method>
-
       <property name="_isCustomizing" readonly="true">
         <getter>
           let root = document.documentElement;
@@ -6451,7 +6342,6 @@
             inBackground = !inBackground;
 
           let targetTab = this._getDragTargetTab(event, true);
-          let userContextId = this.selectedItem.getAttribute("usercontextid");
           let replace = !!targetTab;
           let newIndex = this._getDropIndex(event, true);
           let urls = links.map(link => link.url);
@@ -6461,7 +6351,6 @@
             allowThirdPartyFixup: true,
             targetTab,
             newIndex,
-            userContextId,
           });
         }
 
@@ -6722,14 +6611,6 @@
       -->
       <field name="muteReason">undefined</field>
 
-      <property name="userContextId" readonly="true">
-        <getter>
-          return this.hasAttribute("usercontextid")
-                   ? parseInt(this.getAttribute("usercontextid"))
-                   : 0;
-        </getter>
-      </property>
-
       <property name="soundPlaying" readonly="true">
         <getter>
           return this.getAttribute("soundplaying") == "true";
@@ -6857,27 +6738,6 @@
         ]]>
         </body>
       </method>
-
-      <method name="setUserContextId">
-        <parameter name="aUserContextId"/>
-        <body>
-        <![CDATA[
-          if (aUserContextId) {
-            if (this.linkedBrowser) {
-              this.linkedBrowser.setAttribute("usercontextid", aUserContextId);
-            }
-            this.setAttribute("usercontextid", aUserContextId);
-          } else {
-            if (this.linkedBrowser) {
-              this.linkedBrowser.removeAttribute("usercontextid");
-            }
-            this.removeAttribute("usercontextid");
-          }
-
-          ContextualIdentityService.setTabStyle(this);
-        ]]>
-        </body>
-      </method>
     </implementation>
 
     <handlers>
@@ -7054,30 +6914,9 @@
     <handlers>
       <handler event="popupshowing">
       <![CDATA[
-        if (event.target.getAttribute("id") == "alltabs_containersMenuTab") {
-          createUserContextMenu(event);
-          return;
-        }
-
-        let containersEnabled = Services.prefs.getBoolPref("privacy.userContext.enabled");
-
-        if (event.target.getAttribute("anonid") == "newtab-popup" ||
-            event.target.id == "newtab-popup") {
-          createUserContextMenu(event);
-        } else {
-          document.getElementById("alltabs-popup-separator-1").hidden = !containersEnabled;
-          let containersTab = document.getElementById("alltabs_containersTab");
-
-          containersTab.hidden = !containersEnabled;
-          if (PrivateBrowsingUtils.isWindowPrivate(window)) {
-            containersTab.setAttribute("disabled", "true");
-          }
-
           document.getElementById("alltabs_undoCloseTab").disabled =
             SessionStore.getClosedTabCount(window) == 0;
 
-          var tabcontainer = gBrowser.tabContainer;
-
           // Listen for changes in the tab bar.
           tabcontainer.addEventListener("TabAttrModified", this, false);
           tabcontainer.addEventListener("TabClose", this, false);
@@ -7094,9 +6933,6 @@
 
       <handler event="popuphidden">
       <![CDATA[
-        if (event.target.getAttribute("id") == "alltabs_containersMenuTab") {
-          return;
-        }
 
         // clear out the menu popup and remove the listeners
         for (let i = this.childNodes.length - 1; i > 0; i--) {
@@ -7105,9 +6941,6 @@
             menuItem.tab.mCorrespondingMenuitem = null;
             this.removeChild(menuItem);
           }
-          if (menuItem.hasAttribute("usercontextid")) {
-            this.removeChild(menuItem);
-          }
         }
         var tabcontainer = gBrowser.tabContainer;
         tabcontainer.mTabstrip.removeEventListener("scroll", this, false);
diff --git a/application/basilisk/base/content/utilityOverlay.js b/application/basilisk/base/content/utilityOverlay.js
index c576aef9e..f3ebf3b7e 100644
--- a/application/basilisk/base/content/utilityOverlay.js
+++ b/application/basilisk/base/content/utilityOverlay.js
@@ -5,7 +5,6 @@
 
 // Services = object with smart getters for common XPCOM services
 Components.utils.import("resource://gre/modules/AppConstants.jsm");
-Components.utils.import("resource://gre/modules/ContextualIdentityService.jsm");
 Components.utils.import("resource://gre/modules/Services.jsm");
 Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
 Components.utils.import("resource://gre/modules/PrivateBrowsingUtils.jsm");
@@ -166,7 +165,6 @@ function whereToOpenLink( e, ignoreButton, ignoreAlt )
  *   skipTabAnimation     (boolean)
  *   allowPinnedTabHostChange (boolean)
  *   allowPopups          (boolean)
- *   userContextId        (unsigned int)
  */
 function openUILinkIn(url, where, aAllowThirdPartyFixup, aPostData, aReferrerURI) {
   var params;
@@ -212,7 +210,6 @@ function openLinkIn(url, where, params) {
   var aAllowPinnedTabHostChange = !!params.allowPinnedTabHostChange;
   var aNoReferrer           = params.noReferrer;
   var aAllowPopups          = !!params.allowPopups;
-  var aUserContextId        = params.userContextId;
   var aIndicateErrorPageLoad = params.indicateErrorPageLoad;
   var aPrincipal            = params.originPrincipal;
   var aTriggeringPrincipal  = params.triggeringPrincipal;
@@ -258,7 +255,6 @@ function openLinkIn(url, where, params) {
   function useOAForPrincipal(principal) {
     if (principal && principal.isCodebasePrincipal) {
       let attrs = {
-        userContextId: aUserContextId,
         privateBrowsingId: aIsPrivate || (w && PrivateBrowsingUtils.isWindowPrivate(w)),
       };
       return Services.scriptSecurityManager.createCodebasePrincipal(principal.URI, attrs);
@@ -305,17 +301,12 @@ function openLinkIn(url, where, params) {
                                  createInstance(Ci.nsISupportsPRUint32);
     referrerPolicySupports.data = aReferrerPolicy;
 
-    var userContextIdSupports = Cc["@mozilla.org/supports-PRUint32;1"].
-                                 createInstance(Ci.nsISupportsPRUint32);
-    userContextIdSupports.data = aUserContextId;
-
     sa.appendElement(wuri, /* weak =*/ false);
     sa.appendElement(charset, /* weak =*/ false);
     sa.appendElement(referrerURISupports, /* weak =*/ false);
     sa.appendElement(aPostData, /* weak =*/ false);
     sa.appendElement(allowThirdPartyFixupSupports, /* weak =*/ false);
     sa.appendElement(referrerPolicySupports, /* weak =*/ false);
-    sa.appendElement(userContextIdSupports, /* weak =*/ false);
     sa.appendElement(aPrincipal, /* weak =*/ false);
     sa.appendElement(aTriggeringPrincipal, /* weak =*/ false);
 
@@ -408,8 +399,7 @@ function openLinkIn(url, where, params) {
       flags: flags,
       referrerURI: aNoReferrer ? null : aReferrerURI,
       referrerPolicy: aReferrerPolicy,
-      postData: aPostData,
-      userContextId: aUserContextId
+      postData: aPostData
     });
     browserUsedForLoad = aCurrentBrowser;
     break;
@@ -428,7 +418,6 @@ function openLinkIn(url, where, params) {
       skipAnimation: aSkipTabAnimation,
       allowMixedContent: aAllowMixedContent,
       noReferrer: aNoReferrer,
-      userContextId: aUserContextId,
       originPrincipal: aPrincipal,
       triggeringPrincipal: aTriggeringPrincipal,
     });
@@ -472,74 +461,6 @@ function checkForMiddleClick(node, event) {
   }
 }
 
-// Populate a menu with user-context menu items. This method should be called
-// by onpopupshowing passing the event as first argument.
-function createUserContextMenu(event, isContextMenu = false, excludeUserContextId = 0) {
-  while (event.target.hasChildNodes()) {
-    event.target.removeChild(event.target.firstChild);
-  }
-
-  let bundle = document.getElementById("bundle_browser");
-  let docfrag = document.createDocumentFragment();
-
-  // If we are excluding a userContextId, we want to add a 'no-container' item.
-  if (excludeUserContextId) {
-    let menuitem = document.createElement("menuitem");
-    menuitem.setAttribute("data-usercontextid", "0");
-    menuitem.setAttribute("label", bundle.getString("userContextNone.label"));
-    menuitem.setAttribute("accesskey", bundle.getString("userContextNone.accesskey"));
-
-    // We don't set an oncommand/command attribute because if we have
-    // to exclude a userContextId we are generating the contextMenu and
-    // isContextMenu will be true.
-
-    docfrag.appendChild(menuitem);
-
-    let menuseparator = document.createElement("menuseparator");
-    docfrag.appendChild(menuseparator);
-  }
-
-  ContextualIdentityService.getIdentities().forEach(identity => {
-    if (identity.userContextId == excludeUserContextId) {
-      return;
-    }
-
-    let menuitem = document.createElement("menuitem");
-    menuitem.setAttribute("data-usercontextid", identity.userContextId);
-    menuitem.setAttribute("label", ContextualIdentityService.getUserContextLabel(identity.userContextId));
-
-    if (identity.accessKey) {
-      menuitem.setAttribute("accesskey", bundle.getString(identity.accessKey));
-    }
-
-    menuitem.classList.add("menuitem-iconic");
-    menuitem.setAttribute("data-identity-color", identity.color);
-
-    if (!isContextMenu) {
-      menuitem.setAttribute("command", "Browser:NewUserContextTab");
-    }
-
-    menuitem.setAttribute("data-identity-icon", identity.icon);
-
-    docfrag.appendChild(menuitem);
-  });
-
-  if (!isContextMenu) {
-    docfrag.appendChild(document.createElement("menuseparator"));
-
-    let menuitem = document.createElement("menuitem");
-    menuitem.setAttribute("label",
-                          bundle.getString("userContext.aboutPage.label"));
-    menuitem.setAttribute("accesskey",
-                          bundle.getString("userContext.aboutPage.accesskey"));
-    menuitem.setAttribute("command", "Browser:OpenAboutContainers");
-    docfrag.appendChild(menuitem);
-  }
-
-  event.target.appendChild(docfrag);
-  return true;
-}
-
 // Closes all popups that are ancestors of the node.
 function closeMenus(node)
 {
diff --git a/application/basilisk/components/contextualidentity/content/usercontext.css b/application/basilisk/components/contextualidentity/content/usercontext.css
deleted file mode 100644
index 728275d9f..000000000
--- a/application/basilisk/components/contextualidentity/content/usercontext.css
+++ /dev/null
@@ -1,91 +0,0 @@
-[data-identity-color="blue"] {
-  --identity-tab-color: #0996f8;
-  --identity-icon-color: #00a7e0;
-}
-
-[data-identity-color="turquoise"] {
-  --identity-tab-color: #01bdad;
-  --identity-icon-color: #01bdad;
-}
-
-[data-identity-color="green"] {
-  --identity-tab-color: #57bd35;
-  --identity-icon-color:  #7dc14c;
-}
-
-[data-identity-color="yellow"] {
-  --identity-tab-color: #ffcb00;
-  --identity-icon-color: #ffcb00;
-}
-
-[data-identity-color="orange"] {
-  --identity-tab-color: #ff9216;
-  --identity-icon-color: #ff9216;
-}
-
-[data-identity-color="red"] {
-  --identity-tab-color: #d92215;
-  --identity-icon-color: #d92215;
-}
-
-[data-identity-color="pink"] {
-  --identity-tab-color: #ea385e;
-  --identity-icon-color: #ee5195;
-}
-
-[data-identity-color="purple"] {
-  --identity-tab-color: #7a2f7a;
-  --identity-icon-color: #7a2f7a;
-}
-
-[data-identity-icon="fingerprint"] {
-  --identity-icon: url("chrome://browser/content/usercontext.svg#fingerprint");
-}
-
-[data-identity-icon="briefcase"] {
-  --identity-icon: url("chrome://browser/content/usercontext.svg#briefcase");
-}
-
-[data-identity-icon="dollar"] {
-  --identity-icon: url("chrome://browser/content/usercontext.svg#dollar");
-}
-
-[data-identity-icon="cart"] {
-  --identity-icon: url("chrome://browser/content/usercontext.svg#cart");
-}
-
-[data-identity-icon="circle"] {
-  --identity-icon: url("chrome://browser/content/usercontext.svg#circle");
-}
-
-#userContext-indicator {
-  height: 16px;
-  width: 16px;
-}
-
-#userContext-label {
-  margin-inline-end: 3px;
-  color: var(--identity-tab-color);
-}
-
-#userContext-icons {
-  -moz-box-align: center;
-}
-
-.tabbrowser-tab[usercontextid] {
-  background-image: linear-gradient(to right, transparent 20%, var(--identity-tab-color) 30%, var(--identity-tab-color) 70%, transparent 80%);
-  background-size: auto 2px;
-  background-repeat: no-repeat;
-}
-
-.userContext-icon,
-.menuitem-iconic[data-usercontextid] > .menu-iconic-left > .menu-iconic-icon,
-.subviewbutton[usercontextid] > .toolbarbutton-icon,
-#userContext-indicator {
-  background-image: var(--identity-icon);
-  filter: url(chrome://browser/skin/filters.svg#fill);
-  fill: var(--identity-icon-color);
-  background-size: contain;
-  background-repeat: no-repeat;
-  background-position: center center;
-}
diff --git a/application/basilisk/components/contextualidentity/jar.mn b/application/basilisk/components/contextualidentity/jar.mn
deleted file mode 100644
index 848245949..000000000
--- a/application/basilisk/components/contextualidentity/jar.mn
+++ /dev/null
@@ -1,6 +0,0 @@
-# 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/.
-
-browser.jar:
-    content/browser/usercontext/usercontext.css (content/usercontext.css)
diff --git a/application/basilisk/components/contextualidentity/moz.build b/application/basilisk/components/contextualidentity/moz.build
deleted file mode 100644
index aac3a838c..000000000
--- a/application/basilisk/components/contextualidentity/moz.build
+++ /dev/null
@@ -1,7 +0,0 @@
-# -*- 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/.
-
-JAR_MANIFESTS += ['jar.mn']
diff --git a/application/basilisk/components/customizableui/CustomizableWidgets.jsm b/application/basilisk/components/customizableui/CustomizableWidgets.jsm
index 09b3f167e..401b7ca74 100644
--- a/application/basilisk/components/customizableui/CustomizableWidgets.jsm
+++ b/application/basilisk/components/customizableui/CustomizableWidgets.jsm
@@ -23,8 +23,6 @@ XPCOMUtils.defineLazyModuleGetter(this, "CharsetMenu",
   "resource://gre/modules/CharsetMenu.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
   "resource://gre/modules/PrivateBrowsingUtils.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "ContextualIdentityService",
-  "resource://gre/modules/ContextualIdentityService.jsm");
 
 XPCOMUtils.defineLazyGetter(this, "CharsetBundle", function() {
   const kCharsetBundle = "chrome://global/locale/charsetMenu.properties";
@@ -977,89 +975,6 @@ const CustomizableWidgets = [
       let win = aEvent.view;
       win.MailIntegration.sendLinkForBrowser(win.gBrowser.selectedBrowser)
     }
-  }, {
-    id: "containers-panelmenu",
-    type: "view",
-    viewId: "PanelUI-containers",
-    hasObserver: false,
-    onCreated: function(aNode) {
-      let doc = aNode.ownerDocument;
-      let win = doc.defaultView;
-      let items = doc.getElementById("PanelUI-containersItems");
-
-      let onItemCommand = function (aEvent) {
-        let item = aEvent.target;
-        if (item.hasAttribute("usercontextid")) {
-          let userContextId = parseInt(item.getAttribute("usercontextid"));
-          win.openUILinkIn(win.BROWSER_NEW_TAB_URL, "tab", {userContextId});
-        }
-      };
-      items.addEventListener("command", onItemCommand);
-
-      if (PrivateBrowsingUtils.isWindowPrivate(win)) {
-        aNode.setAttribute("disabled", "true");
-      }
-
-      this.updateVisibility(aNode);
-
-      if (!this.hasObserver) {
-        Services.prefs.addObserver("privacy.userContext.enabled", this, true);
-        this.hasObserver = true;
-      }
-    },
-    onViewShowing: function(aEvent) {
-      let doc = aEvent.target.ownerDocument;
-
-      let items = doc.getElementById("PanelUI-containersItems");
-
-      while (items.firstChild) {
-        items.firstChild.remove();
-      }
-
-      let fragment = doc.createDocumentFragment();
-      let bundle = doc.getElementById("bundle_browser");
-
-      ContextualIdentityService.getIdentities().forEach(identity => {
-        let label = ContextualIdentityService.getUserContextLabel(identity.userContextId);
-
-        let item = doc.createElementNS(kNSXUL, "toolbarbutton");
-        item.setAttribute("label", label);
-        item.setAttribute("usercontextid", identity.userContextId);
-        item.setAttribute("class", "subviewbutton");
-        item.setAttribute("data-identity-color", identity.color);
-        item.setAttribute("data-identity-icon", identity.icon);
-
-        fragment.appendChild(item);
-      });
-
-      fragment.appendChild(doc.createElementNS(kNSXUL, "menuseparator"));
-
-      let item = doc.createElementNS(kNSXUL, "toolbarbutton");
-      item.setAttribute("label", bundle.getString("userContext.aboutPage.label"));
-      item.setAttribute("command", "Browser:OpenAboutContainers");
-      item.setAttribute("class", "subviewbutton");
-      fragment.appendChild(item);
-
-      items.appendChild(fragment);
-    },
-
-    updateVisibility(aNode) {
-      aNode.hidden = !Services.prefs.getBoolPref("privacy.userContext.enabled");
-    },
-
-    observe(aSubject, aTopic, aData) {
-      let {instances} = CustomizableUI.getWidget("containers-panelmenu");
-      for (let {node} of instances) {
-	if (node) {
-	  this.updateVisibility(node);
-	}
-      }
-    },
-
-    QueryInterface: XPCOMUtils.generateQI([
-      Ci.nsISupportsWeakReference,
-      Ci.nsIObserver
-    ]),
   }];
 
 let preferencesButton = {
diff --git a/application/basilisk/components/moz.build b/application/basilisk/components/moz.build
index a7685cbfc..65e8beb76 100644
--- a/application/basilisk/components/moz.build
+++ b/application/basilisk/components/moz.build
@@ -6,7 +6,6 @@
 
 DIRS += [
     'about',
-    'contextualidentity',
     'customizableui',
     'dirprovider',
     'downloads',
diff --git a/application/basilisk/components/preferences/containers.js b/application/basilisk/components/preferences/containers.js
deleted file mode 100644
index 6ca5853f7..000000000
--- a/application/basilisk/components/preferences/containers.js
+++ /dev/null
@@ -1,176 +0,0 @@
-/* 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/. */
-
-Components.utils.import("resource://gre/modules/Services.jsm");
-Components.utils.import("resource://gre/modules/ContextualIdentityService.jsm");
-
-const containersBundle = Services.strings.createBundle("chrome://browser/locale/preferences/containers.properties");
-
-const HTMLNS = "http://www.w3.org/1999/xhtml";
-
-let gContainersManager = {
-  icons: [
-    "fingerprint",
-    "briefcase",
-    "dollar",
-    "cart",
-    "circle"
-  ],
-
-  colors: [
-    "blue",
-    "turquoise",
-    "green",
-    "yellow",
-    "orange",
-    "red",
-    "pink",
-    "purple"
-  ],
-
-  onLoad() {
-    let params = window.arguments[0] || {};
-    this.init(params);
-  },
-
-  init(aParams) {
-    this.userContextId = aParams.userContextId || null;
-    this.identity = aParams.identity;
-
-    if (aParams.windowTitle) {
-      document.title = aParams.windowTitle;
-    }
-
-    const iconWrapper = document.getElementById("iconWrapper");
-    iconWrapper.appendChild(this.createIconButtons());
-
-    const colorWrapper = document.getElementById("colorWrapper");
-    colorWrapper.appendChild(this.createColorSwatches());
-
-    if (this.identity.name) {
-      const name = document.getElementById("name");
-      name.value = this.identity.name;
-      this.checkForm();
-    }
-
-    this.setLabelsMinWidth();
-
-    // This is to prevent layout jank caused by the svgs and outlines rendering at different times
-    document.getElementById("containers-content").removeAttribute("hidden");
-  },
-
-  setLabelsMinWidth() {
-    const labelMinWidth = containersBundle.GetStringFromName("containers.labelMinWidth");
-    const labels = [
-      document.getElementById("nameLabel"),
-      document.getElementById("iconLabel"),
-      document.getElementById("colorLabel")
-    ];
-    for (let label of labels) {
-      label.style.minWidth = labelMinWidth;
-    }
-  },
-
-  uninit() {
-  },
-
-  // Check if name string as to if the form can be submitted
-  checkForm() {
-    const name = document.getElementById("name");
-    let btnApplyChanges = document.getElementById("btnApplyChanges");
-    if (!name.value) {
-      btnApplyChanges.setAttribute("disabled", true);
-    } else {
-      btnApplyChanges.removeAttribute("disabled");
-    }
-  },
-
-  createIconButtons(defaultIcon) {
-    let radiogroup = document.createElement("radiogroup");
-    radiogroup.setAttribute("id", "icon");
-    radiogroup.className = "icon-buttons";
-
-    for (let icon of this.icons) {
-      let iconSwatch = document.createElement("radio");
-      iconSwatch.id = "iconbutton-" + icon;
-      iconSwatch.name = "icon";
-      iconSwatch.type = "radio";
-      iconSwatch.value = icon;
-
-      if (this.identity.icon && this.identity.icon == icon) {
-        iconSwatch.setAttribute("selected", true);
-      }
-
-      iconSwatch.setAttribute("label",
-        containersBundle.GetStringFromName(`containers.${icon}.label`));
-      let iconElement = document.createElement("hbox");
-      iconElement.className = 'userContext-icon';
-      iconElement.setAttribute("data-identity-icon", icon);
-
-      iconSwatch.appendChild(iconElement);
-      radiogroup.appendChild(iconSwatch);
-    }
-
-    return radiogroup;
-  },
-
-  createColorSwatches(defaultColor) {
-    let radiogroup = document.createElement("radiogroup");
-    radiogroup.setAttribute("id", "color");
-
-    for (let color of this.colors) {
-      let colorSwatch = document.createElement("radio");
-      colorSwatch.id = "colorswatch-" + color;
-      colorSwatch.name = "color";
-      colorSwatch.type = "radio";
-      colorSwatch.value = color;
-
-      if (this.identity.color && this.identity.color == color) {
-        colorSwatch.setAttribute("selected", true);
-      }
-
-      colorSwatch.setAttribute("label",
-        containersBundle.GetStringFromName(`containers.${color}.label`));
-      let iconElement = document.createElement("hbox");
-      iconElement.className = 'userContext-icon';
-      iconElement.setAttribute("data-identity-icon", "circle");
-      iconElement.setAttribute("data-identity-color", color);
-
-      colorSwatch.appendChild(iconElement);
-      radiogroup.appendChild(colorSwatch);
-    }
-    return radiogroup;
-  },
-
-  onApplyChanges() {
-    let icon = document.getElementById("icon").value;
-    let color = document.getElementById("color").value;
-    let name = document.getElementById("name").value;
-
-    if (this.icons.indexOf(icon) == -1) {
-      throw "Internal error. The icon value doesn't match.";
-    }
-
-    if (this.colors.indexOf(color) == -1) {
-      throw "Internal error. The color value doesn't match.";
-    }
-
-    if (this.userContextId) {
-      ContextualIdentityService.update(this.userContextId,
-        name,
-        icon,
-        color);
-    } else {
-      ContextualIdentityService.create(name,
-        icon,
-        color);
-    }
-    window.parent.location.reload()
-  },
-
-  onWindowKeyPress(aEvent) {
-    if (aEvent.keyCode == KeyEvent.DOM_VK_ESCAPE)
-      window.close();
-  }
-}
diff --git a/application/basilisk/components/preferences/containers.xul b/application/basilisk/components/preferences/containers.xul
deleted file mode 100644
index 62a775fe4..000000000
--- a/application/basilisk/components/preferences/containers.xul
+++ /dev/null
@@ -1,52 +0,0 @@
-<?xml version="1.0"?>
-
-<!-- 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/. -->
-
-<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
-<?xml-stylesheet href="chrome://browser/skin/preferences/containers.css" type="text/css"?>
-
-<!DOCTYPE dialog SYSTEM "chrome://browser/locale/preferences/containers.dtd" >
-
-<window id="ContainersDialog" class="windowDialog"
-        windowtype="Browser:Permissions"
-        title="&window.title;"
-        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
-        style="width: &window.width;;"
-        onload="gContainersManager.onLoad();"
-        onunload="gContainersManager.uninit();"
-        persist="screenX screenY width height"
-        onkeypress="gContainersManager.onWindowKeyPress(event);">
-
-  <script src="chrome://global/content/treeUtils.js"/>
-  <script src="chrome://browser/content/preferences/containers.js"/>
-
-  <stringbundle id="bundlePreferences"
-                src="chrome://browser/locale/preferences/preferences.properties"/>
-
-  <keyset>
-    <key key="&windowClose.key;" modifiers="accel" oncommand="window.close();"/>
-  </keyset>
-
-  <vbox class="contentPane largeDialogContainer" flex="1" hidden="true" id="containers-content">
-    <description id="permissionsText" control="url"/>
-    <separator class="thin"/>
-    <hbox align="start">
-      <label id="nameLabel" control="url" value="&name.label;" accesskey="&name.accesskey;"/>
-      <textbox id="name" flex="1" onkeyup="gContainersManager.checkForm();" />
-    </hbox>
-    <hbox align="center" id="iconWrapper">
-      <label id="iconLabel" control="url" value="&icon.label;" accesskey="&icon.accesskey;"/>
-    </hbox>
-    <hbox align="center" id="colorWrapper">
-      <label id="colorLabel" control="url" value="&color.label;" accesskey="&color.accesskey;"/>
-    </hbox>
-  </vbox>
-  <vbox>
-    <hbox class="actionButtons" align="right" flex="1">
-      <button id="btnApplyChanges" disabled="true" oncommand="gContainersManager.onApplyChanges();" icon="save"
-              label="&button.ok.label;" accesskey="&button.ok.accesskey;"/>
-    </hbox>
-  </vbox>
-</window>
diff --git a/application/basilisk/components/preferences/cookies.js b/application/basilisk/components/preferences/cookies.js
index c420855f8..4ede5b6e6 100644
--- a/application/basilisk/components/preferences/cookies.js
+++ b/application/basilisk/components/preferences/cookies.js
@@ -7,12 +7,8 @@ const nsICookie = Components.interfaces.nsICookie;
 
 Components.utils.import("resource://gre/modules/AppConstants.jsm");
 Components.utils.import("resource://gre/modules/PluralForm.jsm");
-Components.utils.import("resource://gre/modules/Services.jsm")
 Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
 
-XPCOMUtils.defineLazyModuleGetter(this, "ContextualIdentityService",
-                                  "resource://gre/modules/ContextualIdentityService.jsm");
-
 var gCookiesWindow = {
   _cm               : Components.classes["@mozilla.org/cookiemanager;1"]
                                 .getService(Components.interfaces.nsICookieManager),
@@ -38,10 +34,6 @@ var gCookiesWindow = {
     this._populateList(true);
 
     document.getElementById("filter").focus();
-
-    if (!Services.prefs.getBoolPref("privacy.userContext.enabled")) {
-      document.getElementById("userContextRow").hidden = true;
-    }
   },
 
   uninit: function () {
@@ -82,24 +74,11 @@ var gCookiesWindow = {
                                                aCookieB.originAttributes);
   },
 
-  _isPrivateCookie: function (aCookie) {
-      let { userContextId } = aCookie.originAttributes;
-      if (!userContextId) {
-        // Default identity is public.
-        return false;
-      }
-      return !ContextualIdentityService.getIdentityFromId(userContextId).public;
-  },
-
   observe: function (aCookie, aTopic, aData) {
     if (aTopic != "cookie-changed")
       return;
 
     if (aCookie instanceof Components.interfaces.nsICookie) {
-      if (this._isPrivateCookie(aCookie)) {
-        return;
-      }
-
       var strippedHost = this._makeStrippedHost(aCookie.host);
       if (aData == "changed")
         this._handleCookieChanged(aCookie, strippedHost);
@@ -498,9 +477,6 @@ var gCookiesWindow = {
     while (e.hasMoreElements()) {
       var cookie = e.getNext();
       if (cookie && cookie instanceof Components.interfaces.nsICookie) {
-        if (this._isPrivateCookie(cookie)) {
-          continue;
-        }
 
         var strippedHost = this._makeStrippedHost(cookie.host);
         this._addCookie(strippedHost, cookie, hostCount);
@@ -524,17 +500,9 @@ var gCookiesWindow = {
     return this._bundle.getString("expireAtEndOfSession");
   },
 
-  _getUserContextString: function(aUserContextId) {
-    if (parseInt(aUserContextId) == 0) {
-      return this._bundle.getString("defaultUserContextLabel");
-    }
-
-    return ContextualIdentityService.getUserContextLabel(aUserContextId);
-  },
-
   _updateCookieData: function (aItem) {
     var seln = this._view.selection;
-    var ids = ["name", "value", "host", "path", "isSecure", "expires", "userContext"];
+    var ids = ["name", "value", "host", "path", "isSecure", "expires"];
     var properties;
 
     if (aItem && !aItem.container && seln.count > 0) {
@@ -543,8 +511,7 @@ var gCookiesWindow = {
                      isDomain: aItem.isDomain ? this._bundle.getString("domainColon")
                                               : this._bundle.getString("hostColon"),
                      isSecure: aItem.isSecure ? this._bundle.getString("forSecureOnly")
-                                              : this._bundle.getString("forAnyConnection"),
-                     userContext: this._getUserContextString(aItem.originAttributes.userContextId) };
+                                              : this._bundle.getString("forAnyConnection") };
       for (let id of ids) {
         document.getElementById(id).disabled = false;
       }
@@ -553,7 +520,7 @@ var gCookiesWindow = {
       var noneSelected = this._bundle.getString("noCookieSelected");
       properties = { name: noneSelected, value: noneSelected, host: noneSelected,
                      path: noneSelected, expires: noneSelected,
-                     isSecure: noneSelected, userContext: noneSelected };
+                     isSecure: noneSelected };
       for (let id of ids) {
         document.getElementById(id).disabled = true;
       }
diff --git a/application/basilisk/components/preferences/cookies.xul b/application/basilisk/components/preferences/cookies.xul
index bd60d9346..d5fefdef7 100644
--- a/application/basilisk/components/preferences/cookies.xul
+++ b/application/basilisk/components/preferences/cookies.xul
@@ -85,10 +85,6 @@
             <hbox pack="end"><label id="expiresLabel" control="expires" value="&props.expires.label;"/></hbox>
             <textbox id="expires" readonly="true" class="plain"/>
           </row>
-          <row align="center" id="userContextRow">
-            <hbox pack="end"><label id="userContextLabel" control="userContext" value="&props.container.label;"/></hbox>
-            <textbox id="userContext" readonly="true" class="plain"/>
-          </row>
         </rows>
       </grid>
     </hbox>
diff --git a/application/basilisk/components/preferences/handlers.css b/application/basilisk/components/preferences/handlers.css
index 6af75a08b..d5f100831 100644
--- a/application/basilisk/components/preferences/handlers.css
+++ b/application/basilisk/components/preferences/handlers.css
@@ -10,10 +10,6 @@
   -moz-binding: url("chrome://browser/content/preferences/handlers.xml#handler-selected");
 }
 
-#containersView > richlistitem {
-  -moz-binding: url("chrome://browser/content/preferences/handlers.xml#container");
-}
-
 /**
  * Make the icons appear.
  * Note: we display the icon box for every item whether or not it has an icon
diff --git a/application/basilisk/components/preferences/handlers.xml b/application/basilisk/components/preferences/handlers.xml
index 0c629d759..ad07a493c 100644
--- a/application/basilisk/components/preferences/handlers.xml
+++ b/application/basilisk/components/preferences/handlers.xml
@@ -69,29 +69,6 @@
 
   </binding>
 
-  <binding id="container">
-    <content>
-      <xul:hbox flex="1" equalsize="always">
-        <xul:hbox flex="1" align="center">
-          <xul:hbox xbl:inherits="data-identity-icon=containerIcon,data-identity-color=containerColor" height="24" width="24" class="userContext-icon"/>
-          <xul:label flex="1" crop="end" xbl:inherits="value=containerName"/>
-        </xul:hbox>
-        <xul:hbox flex="1" align="right">
-          <xul:button anonid="preferencesButton"
-                      xbl:inherits="value=userContextId"
-                      onclick="gContainersPane.onPeferenceClick(event.originalTarget)">
-            Preferences
-          </xul:button>
-          <xul:button anonid="removeButton"
-                      xbl:inherits="value=userContextId"
-                      onclick="gContainersPane.onRemoveClick(event.originalTarget)">
-            Remove
-          </xul:button>
-        </xul:hbox>
-      </xul:hbox>
-    </content>
-  </binding>
-
   <binding id="offlineapp"
 	   extends="chrome://global/content/bindings/listbox.xml#listitem">
     <content>
diff --git a/application/basilisk/components/preferences/in-content/containers.js b/application/basilisk/components/preferences/in-content/containers.js
deleted file mode 100644
index 758e45fff..000000000
--- a/application/basilisk/components/preferences/in-content/containers.js
+++ /dev/null
@@ -1,73 +0,0 @@
-/* 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/. */
-
-Components.utils.import("resource://gre/modules/AppConstants.jsm");
-Components.utils.import("resource://gre/modules/ContextualIdentityService.jsm");
-
-const containersBundle = Services.strings.createBundle("chrome://browser/locale/preferences/containers.properties");
-
-const defaultContainerIcon = "fingerprint";
-const defaultContainerColor = "blue";
-
-let gContainersPane = {
-
-  init() {
-    this._list = document.getElementById("containersView");
-
-    document.getElementById("backContainersLink").addEventListener("click", function () {
-      gotoPref("privacy");
-    });
-
-    this._rebuildView();
-  },
-
-  _rebuildView() {
-    const containers = ContextualIdentityService.getIdentities();
-    while (this._list.firstChild) {
-      this._list.firstChild.remove();
-    }
-    for (let container of containers) {
-      let item = document.createElement("richlistitem");
-      item.setAttribute("containerName", ContextualIdentityService.getUserContextLabel(container.userContextId));
-      item.setAttribute("containerIcon", container.icon);
-      item.setAttribute("containerColor", container.color);
-      item.setAttribute("userContextId", container.userContextId);
-
-      this._list.appendChild(item);
-    }
-  },
-
-  onRemoveClick(button) {
-    let userContextId = button.getAttribute("value");
-    ContextualIdentityService.remove(userContextId);
-    this._rebuildView();
-  },
-  onPeferenceClick(button) {
-    this.openPreferenceDialog(button.getAttribute("value"));
-  },
-
-  onAddButtonClick(button) {
-    this.openPreferenceDialog(null);
-  },
-
-  openPreferenceDialog(userContextId) {
-    let identity = {
-      name: "",
-      icon: defaultContainerIcon,
-      color: defaultContainerColor
-    };
-    let title;
-    if (userContextId) {
-      identity = ContextualIdentityService.getIdentityFromId(userContextId);
-      // This is required to get the translation string from defaults
-      identity.name = ContextualIdentityService.getUserContextLabel(identity.userContextId);
-      title = containersBundle.formatStringFromName("containers.updateContainerTitle", [identity.name], 1);
-    }
-
-    const params = { userContextId, identity, windowTitle: title };
-    gSubDialog.open("chrome://browser/content/preferences/containers.xul",
-                     null, params);
-  }
-
-};
diff --git a/application/basilisk/components/preferences/in-content/containers.xul b/application/basilisk/components/preferences/in-content/containers.xul
deleted file mode 100644
index e83bac1c3..000000000
--- a/application/basilisk/components/preferences/in-content/containers.xul
+++ /dev/null
@@ -1,54 +0,0 @@
-# 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/.
-
-<!-- Containers panel -->
-
-<script type="application/javascript"
-        src="chrome://browser/content/preferences/in-content/containers.js"/>
-
-<preferences id="containerPreferences" hidden="true" data-category="paneContainer">
-  <!-- Containers -->
-  <preference id="privacy.userContext.enabled"
-              name="privacy.userContext.enabled"
-              type="bool"/>
-
-</preferences>
-
-<hbox hidden="true"
-      class="container-header-links"
-      data-category="paneContainers">
-  <label class="text-link" id="backContainersLink" value="&backLink.label;" />
-</hbox>
-
-<hbox id="header-containers"
-      class="header"
-      hidden="true"
-      data-category="paneContainers">
-  <label class="header-name" flex="1">&paneContainers.title;</label>
-  <button class="help-button"
-          aria-label="&helpButton.label;"/>
-</hbox>
-
-<!-- Containers -->
-<groupbox id="browserContainersGroup" data-category="paneContainers" hidden="true">
-  <vbox id="browserContainersbox">
-
-    <richlistbox id="containersView" orient="vertical" persist="lastSelectedType"
-                 flex="1">
-      <listheader equalsize="always">
-          <treecol id="typeColumn" label="&label.label;" value="type"
-                   persist="sortDirection"
-                   flex="1" sortDirection="ascending"/>
-          <treecol id="actionColumn" value="action"
-                   persist="sortDirection"
-                   flex="1"/>
-      </listheader>
-    </richlistbox>
-  </vbox>
-  <vbox>
-    <hbox flex="1">
-      <button onclick="gContainersPane.onAddButtonClick();" accesskey="&addButton.accesskey;" label="&addButton.label;"/>
-    </hbox>
-  </vbox>
-</groupbox>
diff --git a/application/basilisk/components/preferences/in-content/jar.mn b/application/basilisk/components/preferences/in-content/jar.mn
index e61a88856..70544f332 100644
--- a/application/basilisk/components/preferences/in-content/jar.mn
+++ b/application/basilisk/components/preferences/in-content/jar.mn
@@ -9,7 +9,6 @@ browser.jar:
 
    content/browser/preferences/in-content/main.js
 *  content/browser/preferences/in-content/privacy.js
-   content/browser/preferences/in-content/containers.js
    content/browser/preferences/in-content/advanced.js
    content/browser/preferences/in-content/applications.js
 *  content/browser/preferences/in-content/content.js
diff --git a/application/basilisk/components/preferences/in-content/preferences.js b/application/basilisk/components/preferences/in-content/preferences.js
index e18ab4b04..35e10c58d 100644
--- a/application/basilisk/components/preferences/in-content/preferences.js
+++ b/application/basilisk/components/preferences/in-content/preferences.js
@@ -61,7 +61,6 @@ function init_all() {
   register_module("paneGeneral", gMainPane);
   register_module("paneSearch", gSearchPane);
   register_module("panePrivacy", gPrivacyPane);
-  register_module("paneContainers", gContainersPane);
   register_module("paneAdvanced", gAdvancedPane);
   register_module("paneApplications", gApplicationsPane);
   register_module("paneContent", gContentPane);
diff --git a/application/basilisk/components/preferences/in-content/preferences.xul b/application/basilisk/components/preferences/in-content/preferences.xul
index 7ec7ef119..093516140 100644
--- a/application/basilisk/components/preferences/in-content/preferences.xul
+++ b/application/basilisk/components/preferences/in-content/preferences.xul
@@ -13,7 +13,6 @@
   href="chrome://browser/content/preferences/handlers.css"?>
 <?xml-stylesheet href="chrome://browser/skin/preferences/applications.css"?>
 <?xml-stylesheet href="chrome://browser/skin/preferences/in-content/search.css"?>
-<?xml-stylesheet href="chrome://browser/skin/preferences/in-content/containers.css"?>
 
 <!DOCTYPE page [
 <!ENTITY % brandDTD SYSTEM "chrome://branding/locale/brand.dtd">
@@ -27,8 +26,6 @@
 <!ENTITY % syncDTD SYSTEM "chrome://browser/locale/preferences/sync.dtd">
 <!ENTITY % securityDTD SYSTEM
   "chrome://browser/locale/preferences/security.dtd">
-<!ENTITY % containersDTD SYSTEM
-  "chrome://browser/locale/preferences/containers.dtd">
 <!ENTITY % sanitizeDTD SYSTEM "chrome://browser/locale/sanitize.dtd">
 <!ENTITY % mainDTD SYSTEM "chrome://browser/locale/preferences/main.dtd">
 <!ENTITY % aboutHomeDTD SYSTEM "chrome://browser/locale/aboutHome.dtd">
@@ -46,7 +43,6 @@
 %syncBrandDTD;
 %syncDTD;
 %securityDTD;
-%containersDTD;
 %sanitizeDTD;
 %mainDTD;
 %aboutHomeDTD;
@@ -134,12 +130,6 @@
         <label class="category-name" flex="1">&panePrivacy.title;</label>
       </richlistitem>
 
-      <richlistitem id="category-containers"
-                    class="category"
-                    value="paneContainers"
-                    helpTopic="prefs-containers"
-                    hidden="true"/>
-
       <richlistitem id="category-security"
                     class="category"
                     value="paneSecurity"
@@ -183,7 +173,6 @@
 #include main.xul
 #include search.xul
 #include privacy.xul
-#include containers.xul
 #include advanced.xul
 #include applications.xul
 #include content.xul
diff --git a/application/basilisk/components/preferences/in-content/privacy.js b/application/basilisk/components/preferences/in-content/privacy.js
index eab606e36..a976fb4fa 100644
--- a/application/basilisk/components/preferences/in-content/privacy.js
+++ b/application/basilisk/components/preferences/in-content/privacy.js
@@ -5,8 +5,6 @@
 Components.utils.import("resource://gre/modules/AppConstants.jsm");
 Components.utils.import("resource://gre/modules/PluralForm.jsm");
 
-XPCOMUtils.defineLazyModuleGetter(this, "ContextualIdentityService",
-                                  "resource://gre/modules/ContextualIdentityService.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "PluralForm",
                                   "resource://gre/modules/PluralForm.jsm");
 
@@ -62,59 +60,6 @@ var gPrivacyPane = {
   },
 
   /**
-   * Show the Containers UI depending on the privacy.userContext.ui.enabled pref.
-   */
-  _initBrowserContainers: function () {
-    if (!Services.prefs.getBoolPref("privacy.userContext.ui.enabled")) {
-      return;
-    }
-
-    let link = document.getElementById("browserContainersLearnMore");
-    link.href = Services.urlFormatter.formatURLPref("app.support.baseURL") + "containers";
-
-    document.getElementById("browserContainersbox").hidden = false;
-
-    document.getElementById("browserContainersCheckbox").checked =
-      Services.prefs.getBoolPref("privacy.userContext.enabled");
-  },
-
-  _checkBrowserContainers: function(event) {
-    let checkbox = document.getElementById("browserContainersCheckbox");
-    if (checkbox.checked) {
-      Services.prefs.setBoolPref("privacy.userContext.enabled", true);
-      return;
-    }
-
-    let count = ContextualIdentityService.countContainerTabs();
-    if (count == 0) {
-      Services.prefs.setBoolPref("privacy.userContext.enabled", false);
-      return;
-    }
-
-    let bundlePreferences = document.getElementById("bundlePreferences");
-
-    let title = bundlePreferences.getString("disableContainersAlertTitle");
-    let message = PluralForm.get(count, bundlePreferences.getString("disableContainersMsg"))
-                            .replace("#S", count)
-    let okButton = PluralForm.get(count, bundlePreferences.getString("disableContainersOkButton"))
-                             .replace("#S", count)
-    let cancelButton = bundlePreferences.getString("disableContainersButton2");
-
-    let buttonFlags = (Ci.nsIPrompt.BUTTON_TITLE_IS_STRING * Ci.nsIPrompt.BUTTON_POS_0) +
-                      (Ci.nsIPrompt.BUTTON_TITLE_IS_STRING * Ci.nsIPrompt.BUTTON_POS_1);
-
-    let rv = Services.prompt.confirmEx(window, title, message, buttonFlags,
-                                       okButton, cancelButton, null, null, {});
-    if (rv == 0) {
-      ContextualIdentityService.closeAllContainerTabs();
-      Services.prefs.setBoolPref("privacy.userContext.enabled", false);
-      return;
-    }
-
-    checkbox.checked = true;
-  },
-
-  /**
    * Sets up the UI for the number of days of history to keep, and updates the
    * label of the "Clear Now..." button.
    */
@@ -136,7 +81,6 @@ var gPrivacyPane = {
     this._initTrackingProtectionPBM();
 #endif
     this._initAutocomplete();
-    this._initBrowserContainers();
 
     setEventListener("privacy.sanitize.sanitizeOnShutdown", "change",
                      gPrivacyPane._updateSanitizeSettingsButton);
@@ -184,10 +128,6 @@ var gPrivacyPane = {
     setEventListener("changeBlockListPBM", "command",
                      gPrivacyPane.showBlockLists);
 #endif
-    setEventListener("browserContainersCheckbox", "command",
-                     gPrivacyPane._checkBrowserContainers);
-    setEventListener("browserContainersSettings", "command",
-                     gPrivacyPane.showContainerSettings);
   },
 
 #ifdef MOZ_SAFE_BROWSING
@@ -489,13 +429,6 @@ var gPrivacyPane = {
   },
 #endif
 
-  /**
-   * Displays container panel for customising and adding containers.
-   */
-  showContainerSettings() {
-    gotoPref("containers");
-  },
-
 #ifdef MOZ_SAFE_BROWSING
   /**
    * Displays the available block lists for tracking protection.
@@ -702,25 +635,4 @@ var gPrivacyPane = {
 
     settingsButton.disabled = !sanitizeOnShutdownPref.value;
    },
-
-  // CONTAINERS
-
-  /*
-   * preferences:
-   *
-   * privacy.userContext.enabled
-   * - true if containers is enabled
-   */
-
-   /**
-    * Enables/disables the Settings button used to configure containers
-    */
-   readBrowserContainersCheckbox: function ()
-   {
-     var pref = document.getElementById("privacy.userContext.enabled");
-     var settings = document.getElementById("browserContainersSettings");
-
-     settings.disabled = !pref.value;
-   }
-
 };
diff --git a/application/basilisk/components/preferences/in-content/privacy.xul b/application/basilisk/components/preferences/in-content/privacy.xul
index e6cdc5dd2..691cd6bf9 100644
--- a/application/basilisk/components/preferences/in-content/privacy.xul
+++ b/application/basilisk/components/preferences/in-content/privacy.xul
@@ -302,28 +302,3 @@
     &suggestionSettings.label;
   </label>
 </groupbox>
-
-<!-- Containers -->
-<groupbox id="browserContainersGroup" data-category="panePrivacy" hidden="true">
-  <vbox id="browserContainersbox" hidden="true">
-    <caption><label>&browserContainersHeader.label;
-      <label id="browserContainersLearnMore" class="text-link"
-             value="&browserContainersLearnMore.label;"/>
-    </label></caption>
-    <hbox align="start">
-      <vbox>
-        <checkbox id="browserContainersCheckbox"
-                  label="&browserContainersEnabled.label;"
-                  accesskey="&browserContainersEnabled.accesskey;"
-                  preference="privacy.userContext.enabled"
-                  onsyncfrompreference="return gPrivacyPane.readBrowserContainersCheckbox();"/>
-      </vbox>
-      <spacer flex="1"/>
-      <vbox>
-        <button id="browserContainersSettings"
-                label="&browserContainersSettings.label;"
-                accesskey="&browserContainersSettings.accesskey;"/>
-      </vbox>
-    </hbox>
-  </vbox>
-</groupbox>
diff --git a/application/basilisk/components/preferences/jar.mn b/application/basilisk/components/preferences/jar.mn
index 5b24e89df..f74be0820 100644
--- a/application/basilisk/components/preferences/jar.mn
+++ b/application/basilisk/components/preferences/jar.mn
@@ -24,8 +24,6 @@ browser.jar:
 *   content/browser/preferences/languages.xul
     content/browser/preferences/languages.js
     content/browser/preferences/permissions.xul
-    content/browser/preferences/containers.xul
-    content/browser/preferences/containers.js
     content/browser/preferences/permissions.js
     content/browser/preferences/sanitize.xul
     content/browser/preferences/sanitize.js
diff --git a/application/basilisk/components/sessionstore/ContentRestore.jsm b/application/basilisk/components/sessionstore/ContentRestore.jsm
index d4972bcaf..8b3867624 100644
--- a/application/basilisk/components/sessionstore/ContentRestore.jsm
+++ b/application/basilisk/components/sessionstore/ContentRestore.jsm
@@ -208,10 +208,6 @@ ContentRestoreInternal.prototype = {
                                   ? Utils.deserializePrincipal(loadArguments.triggeringPrincipal)
                                   : null;
 
-        if (loadArguments.userContextId) {
-          webNavigation.setOriginAttributesBeforeLoading({ userContextId: loadArguments.userContextId });
-        }
-
         webNavigation.loadURIWithOptions(loadArguments.uri, loadArguments.flags,
                                          referrer, referrerPolicy, postData,
                                          null, null, triggeringPrincipal);
diff --git a/application/basilisk/components/sessionstore/SessionHistory.jsm b/application/basilisk/components/sessionstore/SessionHistory.jsm
index 3d28d87db..907a60839 100644
--- a/application/basilisk/components/sessionstore/SessionHistory.jsm
+++ b/application/basilisk/components/sessionstore/SessionHistory.jsm
@@ -64,11 +64,10 @@ var SessionHistoryInternal = {
    *        The docShell that owns the session history.
    */
   collect: function (docShell) {
-    let loadContext = docShell.QueryInterface(Ci.nsILoadContext);
     let webNavigation = docShell.QueryInterface(Ci.nsIWebNavigation);
     let history = webNavigation.sessionHistory.QueryInterface(Ci.nsISHistoryInternal);
 
-    let data = {entries: [], userContextId: loadContext.originAttributes.userContextId };
+    let data = {entries: []};
 
     if (history && history.count > 0) {
       // Loop over the transaction linked list directly so we can get the
diff --git a/application/basilisk/components/sessionstore/SessionStore.jsm b/application/basilisk/components/sessionstore/SessionStore.jsm
index b599bc162..086bb914a 100644
--- a/application/basilisk/components/sessionstore/SessionStore.jsm
+++ b/application/basilisk/components/sessionstore/SessionStore.jsm
@@ -2204,10 +2204,9 @@ var SessionStoreInternal = {
     }
 
     // Create a new tab.
-    let userContextId = aTab.getAttribute("usercontextid");
     let newTab = aTab == aWindow.gBrowser.selectedTab ?
-      aWindow.gBrowser.addTab(null, {relatedToCurrent: true, ownerTab: aTab, userContextId}) :
-      aWindow.gBrowser.addTab(null, {userContextId});
+      aWindow.gBrowser.addTab(null, {relatedToCurrent: true, ownerTab: aTab}) :
+      aWindow.gBrowser.addTab();
 
     // Set tab title to "Connecting..." and start the throbber to pretend we're
     // doing something while actually waiting for data from the frame script.
@@ -2296,7 +2295,7 @@ var SessionStoreInternal = {
 
     // create a new tab
     let tabbrowser = aWindow.gBrowser;
-    let tab = tabbrowser.selectedTab = tabbrowser.addTab(null, state);
+    let tab = tabbrowser.selectedTab = tabbrowser.addTab();
 
     // restore tab content
     this.restoreTab(tab, state);
@@ -3100,31 +3099,13 @@ var SessionStoreInternal = {
     let numVisibleTabs = 0;
 
     for (var t = 0; t < newTabCount; t++) {
-      // When trying to restore into existing tab, we also take the userContextId
-      // into account if present.
-      let userContextId = winData.tabs[t].userContextId;
-      let reuseExisting = t < openTabCount &&
-                          (tabbrowser.tabs[t].getAttribute("usercontextid") == (userContextId || ""));
-      // If the tab is pinned, then we'll be loading it right away, and
-      // there's no need to cause a remoteness flip by loading it initially
-      // non-remote.
-      let forceNotRemote = !winData.tabs[t].pinned;
-      let tab = reuseExisting ? tabbrowser.tabs[t] :
-                                tabbrowser.addTab("about:blank",
-                                                  {skipAnimation: true,
-                                                   forceNotRemote,
-                                                   userContextId,
-                                                   skipBackgroundNotify: true});
-
-      // If we inserted a new tab because the userContextId didn't match with the
-      // open tab, even though `t < openTabCount`, we need to remove that open tab
-      // and put the newly added tab in its place.
-      if (!reuseExisting && t < openTabCount) {
-        tabbrowser.removeTab(tabbrowser.tabs[t]);
-        tabbrowser.moveTabTo(tab, t);
-      }
-
-      tabs.push(tab);
+      tabs.push(t < openTabCount ?
+                tabbrowser.tabs[t] :
+                tabbrowser.addTab("about:blank", {
+                  skipAnimation: true,
+                  forceNotRemote: true,
+                  skipBackgroundNotify: true
+                }));
 
       if (winData.tabs[t].pinned)
         tabbrowser.pinTab(tabs[t]);
@@ -3531,9 +3512,6 @@ var SessionStoreInternal = {
     let uri = activePageData ? activePageData.url || null : null;
     if (aLoadArguments) {
       uri = aLoadArguments.uri;
-      if (aLoadArguments.userContextId) {
-        browser.setAttribute("usercontextid", aLoadArguments.userContextId);
-      }
     }
 
     // We have to mark this tab as restoring first, otherwise
diff --git a/application/basilisk/components/sessionstore/TabState.jsm b/application/basilisk/components/sessionstore/TabState.jsm
index f22c52fe3..ac846031b 100644
--- a/application/basilisk/components/sessionstore/TabState.jsm
+++ b/application/basilisk/components/sessionstore/TabState.jsm
@@ -181,10 +181,6 @@ var TabStateInternal = {
       if (key === "history") {
         tabData.entries = value.entries;
 
-        if (value.hasOwnProperty("userContextId")) {
-          tabData.userContextId = value.userContextId;
-        }
-
         if (value.hasOwnProperty("index")) {
           tabData.index = value.index;
         }
diff --git a/application/basilisk/locales/en-US/chrome/browser/browser.properties b/application/basilisk/locales/en-US/chrome/browser/browser.properties
index f1c39839b..abec30bf1 100644
--- a/application/basilisk/locales/en-US/chrome/browser/browser.properties
+++ b/application/basilisk/locales/en-US/chrome/browser/browser.properties
@@ -638,37 +638,6 @@ e10s.accessibilityNotice.acceptButton.accesskey = O
 e10s.accessibilityNotice.enableAndRestart.label = Enable (Requires Restart)
 e10s.accessibilityNotice.enableAndRestart.accesskey = E
 
-# LOCALIZATION NOTE (userContextPersonal.label,
-#                    userContextWork.label,
-#                    userContextShopping.label,
-#                    userContextBanking.label,
-#                    userContextNone.label):
-# These strings specify the four predefined contexts included in support of the
-# Contextual Identity / Containers project. Each context is meant to represent
-# the context that the user is in when interacting with the site. Different
-# contexts will store cookies and other information from those sites in
-# different, isolated locations. You can enable the feature by typing
-# about:config in the URL bar and changing privacy.userContext.enabled to true.
-# Once enabled, you can open a new tab in a specific context by clicking
-# File > New Container Tab > (1 of 4 contexts). Once opened, you will see these
-# strings on the right-hand side of the URL bar.
-userContextPersonal.label = Personal
-userContextWork.label = Work
-userContextBanking.label = Banking
-userContextShopping.label = Shopping
-userContextNone.label = No Container
-
-userContextPersonal.accesskey = P
-userContextWork.accesskey = W
-userContextBanking.accesskey = B
-userContextShopping.accesskey = S
-userContextNone.accesskey = N
-
-userContext.aboutPage.label = Manage containers
-userContext.aboutPage.accesskey = O
-
-userContextOpenLink.label = Open Link in New %S Tab
-
 muteTab.label = Mute Tab
 muteTab.accesskey = M
 unmuteTab.label = Unmute Tab
diff --git a/application/basilisk/locales/en-US/chrome/browser/preferences/containers.dtd b/application/basilisk/locales/en-US/chrome/browser/preferences/containers.dtd
deleted file mode 100644
index 58eca1ace..000000000
--- a/application/basilisk/locales/en-US/chrome/browser/preferences/containers.dtd
+++ /dev/null
@@ -1,24 +0,0 @@
-<!-- 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/. -->
-
-<!ENTITY label.label          "Name">
-<!ENTITY addButton.label      "Add New Container">
-<!ENTITY addButton.accesskey  "A">
-<!-- &#171; is &laquo; however it's not defined in XML -->
-<!ENTITY backLink.label       "&#171; Go Back to Privacy">
-
-<!ENTITY window.title         "Add New Container">
-<!ENTITY window.width         "45em">
-
-<!ENTITY name.label           "Name:">
-<!ENTITY name.accesskey       "N">
-<!ENTITY icon.label           "Icon:">
-<!ENTITY icon.accesskey       "I">
-<!ENTITY color.label          "Color:">
-<!ENTITY color.accesskey      "o">
-<!ENTITY windowClose.key      "w">
-
-<!ENTITY button.ok.label      "Done">
-<!ENTITY button.ok.accesskey  "D">
-
diff --git a/application/basilisk/locales/en-US/chrome/browser/preferences/containers.properties b/application/basilisk/locales/en-US/chrome/browser/preferences/containers.properties
deleted file mode 100644
index 9866a0659..000000000
--- a/application/basilisk/locales/en-US/chrome/browser/preferences/containers.properties
+++ /dev/null
@@ -1,31 +0,0 @@
-# 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/.
-
-containers.removeButton = Remove
-containers.preferencesButton = Preferences
-containers.colorHeading = Color:
-containers.labelMinWidth = 4rem
-containers.nameLabel = Name:
-containers.namePlaceholder = Enter a container name
-containers.submitButton = Done
-containers.iconHeading = Icon:
-containers.updateContainerTitle = %S Container Preferences
-
-containers.blue.label = Blue
-containers.turquoise.label = Turquoise
-containers.green.label = Green
-containers.yellow.label = Yellow
-containers.orange.label = Orange
-containers.red.label = Red
-containers.pink.label = Pink
-containers.purple.label = Purple
-
-containers.fingerprint.label = Fingerprint
-containers.briefcase.label = Briefcase
-# LOCALIZATION NOTE (containers.dollar.label)
-# String represents a money sign but currently uses a dollar sign so don't change to local currency
-# See Bug 1291672
-containers.dollar.label = Dollar sign
-containers.cart.label = Shopping cart
-containers.circle.label = Dot
diff --git a/application/basilisk/locales/en-US/chrome/browser/preferences/cookies.dtd b/application/basilisk/locales/en-US/chrome/browser/preferences/cookies.dtd
index 5e7df9609..c83331328 100644
--- a/application/basilisk/locales/en-US/chrome/browser/preferences/cookies.dtd
+++ b/application/basilisk/locales/en-US/chrome/browser/preferences/cookies.dtd
@@ -14,7 +14,6 @@
 <!ENTITY     props.path.label               "Path:">
 <!ENTITY     props.secure.label             "Send For:">
 <!ENTITY     props.expires.label            "Expires:">
-<!ENTITY     props.container.label          "Container:">
 
 <!ENTITY     window.title                   "Cookies">
 <!ENTITY     windowClose.key                "w">
diff --git a/application/basilisk/locales/en-US/chrome/browser/preferences/preferences.dtd b/application/basilisk/locales/en-US/chrome/browser/preferences/preferences.dtd
index 7702c8c51..353e627d7 100644
--- a/application/basilisk/locales/en-US/chrome/browser/preferences/preferences.dtd
+++ b/application/basilisk/locales/en-US/chrome/browser/preferences/preferences.dtd
@@ -18,7 +18,6 @@
 <!ENTITY  paneContent.title       "Content">
 <!ENTITY  paneApplications.title  "Applications">
 <!ENTITY  panePrivacy.title       "Privacy">
-<!ENTITY  paneContainers.title    "Container Tabs">
 <!ENTITY  paneSecurity.title      "Security">
 <!ENTITY  paneAdvanced.title      "Advanced">
 
diff --git a/application/basilisk/locales/en-US/chrome/browser/preferences/preferences.properties b/application/basilisk/locales/en-US/chrome/browser/preferences/preferences.properties
index 84fac427d..c0b7e1be0 100644
--- a/application/basilisk/locales/en-US/chrome/browser/preferences/preferences.properties
+++ b/application/basilisk/locales/en-US/chrome/browser/preferences/preferences.properties
@@ -191,17 +191,3 @@ revertNoRestartButton=Revert
 
 restartNow=Restart Now
 restartLater=Restart Later
-
-disableContainersAlertTitle=Close All Container Tabs?
-
-# LOCALIZATION NOTE (disableContainersMsg): Semi-colon list of plural forms.
-# See: http://developer.mozilla.org/en/docs/Localization_and_Plurals
-# #S is the number of container tabs
-disableContainersMsg=If you disable Container Tabs now, #S container tab will be closed. Are you sure you want to disable Container Tabs?;If you disable Container Tabs now, #S container tabs will be closed. Are you sure you want to disable Container Tabs?
-
-# LOCALIZATION NOTE (disableContainersOkButton): Semi-colon list of plural forms.
-# See: http://developer.mozilla.org/en/docs/Localization_and_Plurals
-# #S is the number of container tabs
-disableContainersOkButton=Close #S Container Tab;Close #S Container Tabs
-
-disableContainersButton2=Keep enabled
diff --git a/application/basilisk/locales/en-US/chrome/browser/preferences/privacy.dtd b/application/basilisk/locales/en-US/chrome/browser/preferences/privacy.dtd
index f743c4040..8820e92ab 100644
--- a/application/basilisk/locales/en-US/chrome/browser/preferences/privacy.dtd
+++ b/application/basilisk/locales/en-US/chrome/browser/preferences/privacy.dtd
@@ -110,10 +110,3 @@
 
 <!ENTITY  clearOnCloseSettings.label     "Settings…">
 <!ENTITY  clearOnCloseSettings.accesskey "t">
-
-<!ENTITY  browserContainersHeader.label         "Container Tabs">
-<!ENTITY  browserContainersLearnMore.label      "Learn more">
-<!ENTITY  browserContainersEnabled.label        "Enable Container Tabs">
-<!ENTITY  browserContainersEnabled.accesskey    "n">
-<!ENTITY  browserContainersSettings.label        "Settings…">
-<!ENTITY  browserContainersSettings.accesskey    "i">
diff --git a/application/basilisk/locales/jar.mn b/application/basilisk/locales/jar.mn
index 5c5a72a1f..dfa6d4e00 100644
--- a/application/basilisk/locales/jar.mn
+++ b/application/basilisk/locales/jar.mn
@@ -79,10 +79,8 @@
     locale/browser/preferences/permissions.dtd        (%chrome/browser/preferences/permissions.dtd)
     locale/browser/preferences/preferences.dtd        (%chrome/browser/preferences/preferences.dtd)
     locale/browser/preferences/preferences.properties (%chrome/browser/preferences/preferences.properties)
-    locale/browser/preferences/containers.properties  (%chrome/browser/preferences/containers.properties)
 *   locale/browser/preferences/privacy.dtd            (%chrome/browser/preferences/privacy.dtd)
     locale/browser/preferences/security.dtd           (%chrome/browser/preferences/security.dtd)
-    locale/browser/preferences/containers.dtd         (%chrome/browser/preferences/containers.dtd)
     locale/browser/preferences/sync.dtd               (%chrome/browser/preferences/sync.dtd)
     locale/browser/preferences/tabs.dtd               (%chrome/browser/preferences/tabs.dtd)
     locale/browser/preferences/search.dtd             (%chrome/browser/preferences/search.dtd)
diff --git a/application/basilisk/modules/ContentClick.jsm b/application/basilisk/modules/ContentClick.jsm
index 40101d5d3..4cd665f8c 100644
--- a/application/basilisk/modules/ContentClick.jsm
+++ b/application/basilisk/modules/ContentClick.jsm
@@ -88,11 +88,6 @@ var ContentClick = {
       triggeringPrincipal: json.triggeringPrincipal,
     };
 
-    // The new tab/window must use the same userContextId.
-    if (json.originAttributes.userContextId) {
-      params.userContextId = json.originAttributes.userContextId;
-    }
-
     window.openLinkIn(json.href, where, params);
   }
 };
diff --git a/application/basilisk/themes/shared/incontentprefs/containers.css b/application/basilisk/themes/shared/incontentprefs/containers.css
deleted file mode 100644
index 5446dccce..000000000
--- a/application/basilisk/themes/shared/incontentprefs/containers.css
+++ /dev/null
@@ -1,32 +0,0 @@
-/* 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 ../../../components/contextualidentity/content/usercontext.css
-
-.container-header-links {
-  margin-block-end: 15px;
-}
-
-[data-identity-icon] {
-  margin: 0;
-  margin-inline-end: 16px;
-}
-
-#containersView {
-  border: 0 none;
-  background: transparent;
-}
-
-#containersView richlistitem {
-  margin: 0px;
-  margin-inline-end: 8px;
-  padding: 0;
-  padding-block-end: 8px;
-  border-block-end: 1px solid var(--in-content-header-border-color);
-}
-
-#containersView richlistitem:last-of-type {
-  border-block-end: 0 none;
-  margin-block-end: 8px;
-}
diff --git a/application/basilisk/themes/shared/incontentprefs/preferences.inc.css b/application/basilisk/themes/shared/incontentprefs/preferences.inc.css
index 0e62660de..20ea98327 100644
--- a/application/basilisk/themes/shared/incontentprefs/preferences.inc.css
+++ b/application/basilisk/themes/shared/incontentprefs/preferences.inc.css
@@ -237,8 +237,7 @@ treecol {
 /* Privacy pane */
 
 #trackingProtectionPBMLearnMore,
-#trackingProtectionLearnMore,
-#browserContainersLearnMore {
+#trackingProtectionLearnMore {
   margin-inline-start: 1.5em !important;
   margin-top: 0;
   font-weight: normal;
diff --git a/application/basilisk/themes/shared/jar.inc.mn b/application/basilisk/themes/shared/jar.inc.mn
index 361edd311..5750d2dc5 100644
--- a/application/basilisk/themes/shared/jar.inc.mn
+++ b/application/basilisk/themes/shared/jar.inc.mn
@@ -73,8 +73,6 @@
   skin/classic/browser/preferences/in-content/favicon.ico      (../shared/incontentprefs/favicon.ico)
   skin/classic/browser/preferences/in-content/icons.svg        (../shared/incontentprefs/icons.svg)
   skin/classic/browser/preferences/in-content/search.css       (../shared/incontentprefs/search.css)
-* skin/classic/browser/preferences/in-content/containers.css   (../shared/incontentprefs/containers.css)
-* skin/classic/browser/preferences/containers.css              (../shared/preferences/containers.css)
   skin/classic/browser/fxa/default-avatar.svg                  (../shared/fxa/default-avatar.svg)
   skin/classic/browser/fxa/logo.png                            (../shared/fxa/logo.png)
   skin/classic/browser/fxa/logo@2x.png                         (../shared/fxa/logo@2x.png)
diff --git a/application/basilisk/themes/shared/preferences/containers.css b/application/basilisk/themes/shared/preferences/containers.css
deleted file mode 100644
index 3fb965331..000000000
--- a/application/basilisk/themes/shared/preferences/containers.css
+++ /dev/null
@@ -1,53 +0,0 @@
-/* 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 ../../../components/contextualidentity/content/usercontext.css
-
-:root {
-  --preference-selected-color: #0996f8;
-  --preference-unselected-color: #333;
-  --preference-active-color: #858585;
-}
-
-radiogroup {
-  display: flex;
-  margin-inline-start: 0.35rem;
-}
-
-radio {
-  flex: auto;
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  -moz-user-select: none;
-  outline: 2px solid transparent;
-  outline-offset: 4px;
-  -moz-outline-radius: 100%;
-  min-block-size: 24px;
-  min-inline-size: 24px;
-  border-radius: 50%;
-  padding: 2px;
-  margin: 10px;
-}
-
-.icon-buttons > radio > [data-identity-icon] {
-  fill: #4d4d4d;
-}
-
-radio > [data-identity-icon] {
-  inline-size: 22px;
-  block-size: 22px;
-}
-
-radio[selected=true] {
-  outline-color: var(--preference-unselected-color);
-}
-
-radio[focused=true] {
-  outline-color: var(--preference-selected-color);
-}
-
-radio:hover:active {
-  outline-color: var(--preference-active-color);
-}
diff --git a/application/palemoon/app/profile/palemoon.js b/application/palemoon/app/profile/palemoon.js
index 85dc41c15..bd1b62cc3 100644
--- a/application/palemoon/app/profile/palemoon.js
+++ b/application/palemoon/app/profile/palemoon.js
@@ -1089,8 +1089,6 @@ pref("browser.pagethumbnails.capturing_disabled", false);
 // enables showing basic placeholders for missing thumbnails
 pref("browser.newtabpage.thumbnailPlaceholder", false);
 
-pref("privacy.usercontext.about_newtab_segregation.enabled", false);
-
 // number of columns of newtab grid
 pref("browser.newtabpage.columns", 4);
 
diff --git a/application/palemoon/base/content/browser.js b/application/palemoon/base/content/browser.js
index 1e7129272..7672fa3a8 100644
--- a/application/palemoon/base/content/browser.js
+++ b/application/palemoon/base/content/browser.js
@@ -5338,9 +5338,6 @@ function handleDroppedLink(event, urlOrLinks, name)
 
   let lastLocationChange = gBrowser.selectedBrowser.lastLocationChange;
 
-  let userContextId = gBrowser.selectedBrowser
-                      .getAttribute("usercontextid") || 0;
-
   let inBackground = Services.prefs.getBoolPref("browser.tabs.loadInBackground");
   if (event.shiftKey)
     inBackground = !inBackground;
@@ -5359,7 +5356,6 @@ function handleDroppedLink(event, urlOrLinks, name)
         replace: true,
         allowThirdPartyFixup: false,
         postDatas,
-        userContextId,
       });
     }
   });
diff --git a/application/palemoon/base/content/content.js b/application/palemoon/base/content/content.js
index 653dac3e3..211a24a8b 100644
--- a/application/palemoon/base/content/content.js
+++ b/application/palemoon/base/content/content.js
@@ -139,7 +139,6 @@ var handleContentContextMenu = function (event) {
   let selectionInfo = BrowserUtils.getSelectionDetails(content);
 
   let loadContext = docShell.QueryInterface(Ci.nsILoadContext);
-  let userContextId = loadContext.originAttributes.userContextId;
 
   let browser = docShell.chromeEventHandler;
   let mainWin = browser.ownerGlobal;
@@ -160,7 +159,6 @@ var handleContentContextMenu = function (event) {
     selectionInfo: selectionInfo,
     loginFillInfo,
     parentAllowsMixedContent,
-    userContextId,
   };
 }
 
diff --git a/application/palemoon/base/content/tabbrowser.xml b/application/palemoon/base/content/tabbrowser.xml
index cbe029af0..868179b5d 100644
--- a/application/palemoon/base/content/tabbrowser.xml
+++ b/application/palemoon/base/content/tabbrowser.xml
@@ -737,8 +737,7 @@
 
                 let autocomplete = this.mTabBrowser._placesAutocomplete;
                 if (this.mBrowser.registeredOpenURI) {
-                  autocomplete.unregisterOpenPage(this.mBrowser.registeredOpenURI,
-                                                  this.mBrowser.getAttribute("usercontextid") || 0);
+                  autocomplete.unregisterOpenPage(this.mBrowser.registeredOpenURI);
                   delete this.mBrowser.registeredOpenURI;
                 }
                 // Tabs in private windows aren't registered as "Open" so
@@ -746,8 +745,7 @@
                 if (!isBlankPageURL(aLocation.spec) &&
                     (!PrivateBrowsingUtils.isWindowPrivate(window) ||
                     PrivateBrowsingUtils.permanentPrivateBrowsing)) {
-                  autocomplete.registerOpenPage(aLocation,
-                                                this.mBrowser.getAttribute("usercontextid") || 0);
+                  autocomplete.registerOpenPage(aLocation);
                   this.mBrowser.registeredOpenURI = aLocation;
                 }
               }
@@ -1383,7 +1381,6 @@
           let aTargetTab;
           let aNewIndex = -1;
           let aPostDatas = [];
-          let aUserContextId;
           if (arguments.length == 2 &&
               typeof arguments[1] == "object") {
             let params = arguments[1];
@@ -1394,7 +1391,6 @@
             aNewIndex             = typeof params.newIndex === "number" ?
                                     params.newIndex : aNewIndex;
             aPostDatas            = params.postDatas || aPostDatas;
-            aUserContextId        = params.userContextId;
           }
 
           if (!aURIs.length)
@@ -1443,8 +1439,7 @@
               ownerTab: owner,
               skipAnimation: multiple,
               allowThirdPartyFixup: aAllowThirdPartyFixup,
-              postData: aPostDatas[0],
-              userContextId: aUserContextId
+              postData: aPostDatas[0]
             });
             if (aNewIndex !== -1) {
               this.moveTabTo(firstTabAdded, aNewIndex);
@@ -1457,8 +1452,7 @@
             let tab = this.addTab(aURIs[i], {
               skipAnimation: true,
               allowThirdPartyFixup: aAllowThirdPartyFixup,
-              postData: aPostDatas[i],
-              userContextId: aUserContextId
+              postData: aPostDatas[i]
             });
             if (targetTabIndex !== -1)
               this.moveTabTo(tab, ++tabNum);
@@ -2059,8 +2053,7 @@
             this.mTabListeners[aTab._tPos].destroy();
 
             if (browser.registeredOpenURI && !aTabWillBeMoved) {
-              this._placesAutocomplete.unregisterOpenPage(browser.registeredOpenURI,
-                                                          browser.getAttribute("usercontextid") || 0);
+              this._placesAutocomplete.unregisterOpenPage(browser.registeredOpenURI);
               delete browser.registeredOpenURI;
             }
 
@@ -2428,8 +2421,7 @@
           <![CDATA[
             // If the current URI is registered as open remove it from the list.
             if (aOurBrowser.registeredOpenURI) {
-              this._placesAutocomplete.unregisterOpenPage(aOurBrowser.registeredOpenURI,
-                                                          aOurBrowser.getAttribute("usercontextid") || 0);
+              this._placesAutocomplete.unregisterOpenPage(aOurBrowser.registeredOpenURI);
               delete aOurBrowser.registeredOpenURI;
             }
 
@@ -3339,8 +3331,7 @@
           for (var i = 0; i < this.mTabListeners.length; ++i) {
             let browser = this.getBrowserAtIndex(i);
             if (browser.registeredOpenURI) {
-              this._placesAutocomplete.unregisterOpenPage(browser.registeredOpenURI,
-                                                          browser.getAttribute("usercontextid") || 0);
+              this._placesAutocomplete.unregisterOpenPage(browser.registeredOpenURI);
               delete browser.registeredOpenURI;
             }
             browser.webProgress.removeProgressListener(this.mTabFilters[i]);
@@ -4799,8 +4790,6 @@
             inBackground = !inBackground;
 
           let targetTab = this._getDragTargetTab(event);
-          let userContextId = this.selectedItem
-                              .getAttribute("usercontextid") || 0;
           let replace = !(!targetTab || dropEffect == "copy");
           let newIndex = this._getDropIndex(event);
           let urls = links.map(link => link.url);
@@ -4810,7 +4799,6 @@
             allowThirdPartyFixup: true,
             targetTab,
             newIndex,
-            userContextId,
           });
         }
 
diff --git a/devtools/client/responsive.html/docs/browser-swap.md b/devtools/client/responsive.html/docs/browser-swap.md
index 75055ad4e..f4f8322cb 100644
--- a/devtools/client/responsive.html/docs/browser-swap.md
+++ b/devtools/client/responsive.html/docs/browser-swap.md
@@ -96,11 +96,8 @@ browsers are swapped.
 Browser attributes `gBrowser.swapBrowsersAndCloseOther` transfers between
 browsers:
 
-* `usercontextid`
-
 Tab attributes `gBrowser.swapBrowsersAndCloseOther` transfers between tabs:
 
-* `usercontextid`
 * `muted`
 * `soundplaying`
 * `busy`
diff --git a/devtools/client/responsive.html/manager.js b/devtools/client/responsive.html/manager.js
index a3fbed366..97ef8ad6d 100644
--- a/devtools/client/responsive.html/manager.js
+++ b/devtools/client/responsive.html/manager.js
@@ -76,11 +76,6 @@ const ResponsiveUIManager = exports.ResponsiveUIManager = {
       this.showRemoteOnlyNotification(window, tab, options);
       return promise.reject(new Error("RDM only available for remote tabs."));
     }
-    // Remove this once we support this case in bug 1306975.
-    if (tab.linkedBrowser.hasAttribute("usercontextid")) {
-      this.showNoContainerTabsNotification(window, tab, options);
-      return promise.reject(new Error("RDM not available for container tabs."));
-    }
     if (!this.isActiveForTab(tab)) {
       this.initMenuCheckListenerFor(window);
 
@@ -218,16 +213,7 @@ const ResponsiveUIManager = exports.ResponsiveUIManager = {
     }
   }),
 
-  showRemoteOnlyNotification(window, tab, options) {
-    this.showErrorNotification(window, tab, options, getStr("responsive.remoteOnly"));
-  },
-
-  showNoContainerTabsNotification(window, tab, options) {
-    this.showErrorNotification(window, tab, options,
-                               getStr("responsive.noContainerTabs"));
-  },
-
-  showErrorNotification(window, tab, { command } = {}, msg) {
+  showRemoteOnlyNotification(window, tab, { command } = {}) {
     // Default to using the browser's per-tab notification box
     let nbox = window.gBrowser.getNotificationBox(tab.linkedBrowser);
 
diff --git a/devtools/client/styleeditor/test/browser.ini b/devtools/client/styleeditor/test/browser.ini
index 4a84d45e6..ba935e1dd 100644
--- a/devtools/client/styleeditor/test/browser.ini
+++ b/devtools/client/styleeditor/test/browser.ini
@@ -77,7 +77,6 @@ support-files =
 [browser_styleeditor_init.js]
 [browser_styleeditor_inline_friendly_names.js]
 [browser_styleeditor_loading.js]
-[browser_styleeditor_loading_with_containers.js]
 [browser_styleeditor_media_sidebar.js]
 [browser_styleeditor_media_sidebar_links.js]
 skip-if = e10s && debug # Bug 1252201 - Docshell leak on debug e10s
diff --git a/devtools/client/styleeditor/test/browser_styleeditor_loading_with_containers.js b/devtools/client/styleeditor/test/browser_styleeditor_loading_with_containers.js
deleted file mode 100644
index a00628c8b..000000000
--- a/devtools/client/styleeditor/test/browser_styleeditor_loading_with_containers.js
+++ /dev/null
@@ -1,63 +0,0 @@
-/* vim: set ts=2 et sw=2 tw=80: */
-/* Any copyright is dedicated to the Public Domain.
-   http://creativecommons.org/publicdomain/zero/1.0/ */
-
-"use strict";
-
-// Test that the stylesheets can be loaded correctly with containers
-// (bug 1282660).
-
-const TESTCASE_URI = TEST_BASE_HTTP + "simple.html";
-const EXPECTED_SHEETS = [
-  {
-    sheetIndex: 0,
-    name: /^simple.css$/,
-    rules: 1,
-    active: true
-  }, {
-    sheetIndex: 1,
-    name: /^<.*>$/,
-    rules: 3,
-    active: false
-  }
-];
-
-add_task(function* () {
-  // Using the personal container.
-  let userContextId = 1;
-  let { tab } = yield* openTabInUserContext(TESTCASE_URI, userContextId);
-  let { ui } = yield openStyleEditor(tab);
-
-  is(ui.editors.length, 2, "The UI contains two style sheets.");
-  checkSheet(ui.editors[0], EXPECTED_SHEETS[0]);
-  checkSheet(ui.editors[1], EXPECTED_SHEETS[1]);
-});
-
-function* openTabInUserContext(uri, userContextId) {
-  // Open the tab in the correct userContextId.
-  let tab = gBrowser.addTab(uri, {userContextId});
-
-  // Select tab and make sure its browser is focused.
-  gBrowser.selectedTab = tab;
-  tab.ownerDocument.defaultView.focus();
-
-  let browser = gBrowser.getBrowserForTab(tab);
-  yield BrowserTestUtils.browserLoaded(browser);
-  return {tab, browser};
-}
-
-function checkSheet(editor, expected) {
-  is(editor.styleSheet.styleSheetIndex, expected.sheetIndex,
-    "Style sheet has correct index.");
-
-  let summary = editor.summary;
-  let name = summary.querySelector(".stylesheet-name > label")
-                    .getAttribute("value");
-  ok(expected.name.test(name), "The name '" + name + "' is correct.");
-
-  let ruleCount = summary.querySelector(".stylesheet-rule-count").textContent;
-  is(parseInt(ruleCount, 10), expected.rules, "the rule count is correct");
-
-  is(summary.classList.contains("splitview-active"), expected.active,
-    "The active status for this sheet is correct.");
-}
diff --git a/devtools/client/webconsole/new-console-output/test/fixtures/stubs/consoleApi.js b/devtools/client/webconsole/new-console-output/test/fixtures/stubs/consoleApi.js
index 26e95fe39..d9662c4fd 100644
--- a/devtools/client/webconsole/new-console-output/test/fixtures/stubs/consoleApi.js
+++ b/devtools/client/webconsole/new-console-output/test/fixtures/stubs/consoleApi.js
@@ -657,8 +657,7 @@ stubPackets.set("console.log('foobar', 'test')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -690,8 +689,7 @@ stubPackets.set("console.log(undefined)", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -721,8 +719,7 @@ stubPackets.set("console.warn('danger, will robinson!')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -754,8 +751,7 @@ stubPackets.set("console.log(NaN)", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -787,8 +783,7 @@ stubPackets.set("console.log(null)", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -818,8 +813,7 @@ stubPackets.set("console.log('鼬')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -847,8 +841,7 @@ stubPackets.set("console.clear()", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086275587,
@@ -881,8 +874,7 @@ stubPackets.set("console.count('bar')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086277812,
@@ -933,8 +925,7 @@ stubPackets.set("console.assert(false, {message: 'foobar'})", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -973,8 +964,7 @@ stubPackets.set("console.log('hello \nfrom \rthe \"string world!')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -1004,8 +994,7 @@ stubPackets.set("console.log('úṇĩçödê țĕșť')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [],
@@ -1047,8 +1036,7 @@ stubPackets.set("console.dirxml(window)", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086285483,
@@ -1076,8 +1064,7 @@ stubPackets.set("console.trace()", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086287286,
@@ -1130,8 +1117,7 @@ stubPackets.set("console.time('bar')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086289137,
@@ -1164,8 +1150,7 @@ stubPackets.set("console.timeEnd('bar')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086289138,
@@ -1198,8 +1183,7 @@ stubPackets.set("console.table('bar')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086290984,
@@ -1246,8 +1230,7 @@ stubPackets.set("console.table(['a', 'b', 'c'])", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086292762,
@@ -1277,8 +1260,7 @@ stubPackets.set("console.group('bar')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086294628,
@@ -1308,8 +1290,7 @@ stubPackets.set("console.groupEnd('bar')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086294630,
@@ -1339,8 +1320,7 @@ stubPackets.set("console.groupCollapsed('foo')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086296567,
@@ -1370,8 +1350,7 @@ stubPackets.set("console.groupEnd('foo')", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086296570,
@@ -1399,8 +1378,7 @@ stubPackets.set("console.group()", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086298462,
@@ -1428,8 +1406,7 @@ stubPackets.set("console.groupEnd()", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"timeStamp": 1477086298464,
@@ -1460,8 +1437,7 @@ stubPackets.set("console.log(%cfoobar)", {
 			"appId": 0,
 			"firstPartyDomain": "",
 			"inIsolatedMozBrowser": false,
-			"privateBrowsingId": 0,
-			"userContextId": 0
+			"privateBrowsingId": 0
 		},
 		"private": false,
 		"styles": [
diff --git a/devtools/server/actors/stylesheets.js b/devtools/server/actors/stylesheets.js
index 7fcbca8c4..f484a5976 100644
--- a/devtools/server/actors/stylesheets.js
+++ b/devtools/server/actors/stylesheets.js
@@ -451,21 +451,10 @@ var StyleSheetActor = protocol.ActorClassWithSpec(styleSheetSpec, {
     let options = {
       loadFromCache: true,
       policy: Ci.nsIContentPolicy.TYPE_INTERNAL_STYLESHEET,
+      window: this.window,
       charset: this._getCSSCharset()
     };
 
-    // Bug 1282660 - We use the system principal to load the default internal
-    // stylesheets instead of the content principal since such stylesheets
-    // require system principal to load. At meanwhile, we strip the loadGroup
-    // for preventing the assertion of the userContextId mismatching.
-    // The default internal stylesheets load from the 'resource:' URL.
-    // Bug 1287607, 1291321 - 'chrome' and 'file' protocols should also be handled in the
-    // same way.
-    if (!/^(chrome|file|resource):\/\//.test(this.href)) {
-      options.window = this.window;
-      options.principal = this.document.nodePrincipal;
-    }
-
     return fetch(this.href, options).then(({ content }) => {
       this.text = content;
       return content;
diff --git a/toolkit/components/places/UnifiedComplete.js b/toolkit/components/places/UnifiedComplete.js
index 2efae9cbe..ec5f91111 100644
--- a/toolkit/components/places/UnifiedComplete.js
+++ b/toolkit/components/places/UnifiedComplete.js
@@ -124,9 +124,7 @@ function defaultQuery(conditions = "") {
             h.visit_count, h.typed, h.id, t.open_count, h.frecency
      FROM moz_places h
      LEFT JOIN moz_favicons f ON f.id = h.favicon_id
-     LEFT JOIN moz_openpages_temp t
-            ON t.url = h.url
-           AND t.userContextId = :userContextId
+     LEFT JOIN moz_openpages_temp t ON t.url = h.url
      WHERE h.frecency <> 0
        AND AUTOCOMPLETE_MATCH(:searchString, h.url,
                               CASE WHEN bookmarked THEN
@@ -150,7 +148,6 @@ const SQL_SWITCHTAB_QUERY =
    FROM moz_openpages_temp t
    LEFT JOIN moz_places h ON h.url_hash = hash(t.url) AND h.url = t.url
    WHERE h.id IS NULL
-     AND t.userContextId = :userContextId
      AND AUTOCOMPLETE_MATCH(:searchString, t.url, t.url, NULL,
                             NULL, NULL, NULL, t.open_count,
                             :matchBehavior, :searchBehavior)
@@ -170,9 +167,7 @@ const SQL_ADAPTIVE_QUERY =
    ) AS i
    JOIN moz_places h ON h.id = i.place_id
    LEFT JOIN moz_favicons f ON f.id = h.favicon_id
-   LEFT JOIN moz_openpages_temp t
-          ON t.url = h.url
-         AND t.userContextId = :userContextId
+   LEFT JOIN moz_openpages_temp t ON t.url = h.url
    WHERE AUTOCOMPLETE_MATCH(NULL, h.url,
                             IFNULL(btitle, h.title), tags,
                             h.visit_count, h.typed, bookmarked,
@@ -301,17 +296,15 @@ XPCOMUtils.defineLazyServiceGetter(this, "textURIService",
 XPCOMUtils.defineLazyGetter(this, "SwitchToTabStorage", () => Object.seal({
   _conn: null,
   // Temporary queue used while the database connection is not available.
-  _queue: new Map(),
+  _queue: new Set(),
   initDatabase: Task.async(function* (conn) {
     // To reduce IO use an in-memory table for switch-to-tab tracking.
     // Note: this should be kept up-to-date with the definition in
     //       nsPlacesTables.h.
     yield conn.execute(
       `CREATE TEMP TABLE moz_openpages_temp (
-         url TEXT,
-         userContextId INTEGER,
-         open_count INTEGER,
-         PRIMARY KEY (url, userContextId)
+         url TEXT PRIMARY KEY,
+         open_count INTEGER
        )`);
 
     // Note: this should be kept up-to-date with the definition in
@@ -322,64 +315,44 @@ XPCOMUtils.defineLazyGetter(this, "SwitchToTabStorage", () => Object.seal({
        WHEN NEW.open_count = 0
        BEGIN
          DELETE FROM moz_openpages_temp
-         WHERE url = NEW.url
-           AND userContextId = NEW.userContextId;
+         WHERE url = NEW.url;
        END`);
 
     this._conn = conn;
 
     // Populate the table with the current cache contents...
-    for (let [userContextId, uris] of this._queue) {
-      for (let uri of uris) {
-        this.add(uri, userContextId);
-      }
-    }
+    this._queue.forEach(this.add, this);
 
     // ...then clear it to avoid double additions.
     this._queue.clear();
   }),
 
-  add(uri, userContextId) {
+  add: function (uri) {
     if (!this._conn) {
-      if (!this._queue.has(userContextId)) {
-        this._queue.set(userContextId, new Set());
-      }
-      this._queue.get(userContextId).add(uri);
+      this._queue.add(uri);
       return;
     }
     this._conn.executeCached(
-      `INSERT OR REPLACE INTO moz_openpages_temp (url, userContextId, open_count)
-         VALUES ( :url,
-                  :userContextId,
-                  IFNULL( ( SELECT open_count + 1
-                            FROM moz_openpages_temp
-                            WHERE url = :url
-                            AND userContextId = :userContextId ),
-                          1
-                        )
+      `INSERT OR REPLACE INTO moz_openpages_temp (url, open_count)
+         VALUES ( :url, IFNULL( (SELECT open_count + 1
+                                  FROM moz_openpages_temp
+                                  WHERE url = :url),
+                                  1
+                              )
                 )`
-    , { url: uri.spec, userContextId });
+    , { url: uri.spec });
   },
 
-  delete(uri, userContextId) {
+  delete: function (uri) {
     if (!this._conn) {
-      // This should not happen.
-      if (!this._queue.has(userContextId)) {
-        throw new Error("Unknown userContextId!");
-      }
-
-      this._queue.get(userContextId).delete(uri);
-      if (this._queue.get(userContextId).size == 0) {
-        this._queue.delete(userContextId);
-      }
+      this._queue.delete(uri);
       return;
     }
     this._conn.executeCached(
       `UPDATE moz_openpages_temp
        SET open_count = open_count - 1
-       WHERE url = :url
-       AND userContextId = :userContextId`
-    , { url: uri.spec, userContextId });
+       WHERE url = :url`
+    , { url: uri.spec });
   },
 
   shutdown: function () {
@@ -1781,7 +1754,6 @@ Search.prototype = {
         // We only want to search the tokens that we are left with - not the
         // original search string.
         searchString: this._searchTokens.join(" "),
-        userContextId: this._userContextId,
         // Limit the query to the the maximum number of desired results.
         // This way we can avoid doing more work than needed.
         maxResults: Prefs.maxRichResults
@@ -1805,7 +1777,6 @@ Search.prototype = {
         // We only want to search the tokens that we are left with - not the
         // original search string.
         searchString: this._searchTokens.join(" "),
-        userContextId: this._userContextId,
         maxResults: Prefs.maxRichResults
       }
     ];
@@ -1825,8 +1796,7 @@ Search.prototype = {
         search_string: this._searchString,
         query_type: QUERYTYPE_FILTERED,
         matchBehavior: this._matchBehavior,
-        searchBehavior: this._behavior,
-        userContextId: this._userContextId,
+        searchBehavior: this._behavior
       }
     ];
   },
@@ -2010,12 +1980,12 @@ UnifiedComplete.prototype = {
 
   // mozIPlacesAutoComplete
 
-  registerOpenPage(uri, userContextId) {
-    SwitchToTabStorage.add(uri, userContextId);
+  registerOpenPage: function PAC_registerOpenPage(uri) {
+    SwitchToTabStorage.add(uri);
   },
 
-  unregisterOpenPage(uri, userContextId) {
-    SwitchToTabStorage.delete(uri, userContextId);
+  unregisterOpenPage: function PAC_unregisterOpenPage(uri) {
+    SwitchToTabStorage.delete(uri);
   },
 
   // nsIAutoCompleteSearch
diff --git a/toolkit/components/places/mozIPlacesAutoComplete.idl b/toolkit/components/places/mozIPlacesAutoComplete.idl
index 7f3247fdc..6ff82e667 100644
--- a/toolkit/components/places/mozIPlacesAutoComplete.idl
+++ b/toolkit/components/places/mozIPlacesAutoComplete.idl
@@ -116,10 +116,8 @@ interface mozIPlacesAutoComplete : nsISupports
    *
    * @param aURI
    *        The URI to register as an open page.
-   * @param aUserContextId
-   *        The Container Id of the tab.
    */
-  void registerOpenPage(in nsIURI aURI, in uint32_t aUserContextId);
+  void registerOpenPage(in nsIURI aURI);
 
   /**
    * Mark a page as no longer being open (either by closing the window or tab,
@@ -131,8 +129,6 @@ interface mozIPlacesAutoComplete : nsISupports
    *
    * @param aURI
    *        The URI to unregister as an open page.
-   * @param aUserContextId
-   *        The Container Id of the tab.
    */
-  void unregisterOpenPage(in nsIURI aURI, in uint32_t aUserContextId);
+  void unregisterOpenPage(in nsIURI aURI);
 };
diff --git a/toolkit/components/places/nsPlacesTables.h b/toolkit/components/places/nsPlacesTables.h
index aca92735e..0b6e414fb 100644
--- a/toolkit/components/places/nsPlacesTables.h
+++ b/toolkit/components/places/nsPlacesTables.h
@@ -133,10 +133,8 @@
 //       nsPlacesAutoComplete.js.
 #define CREATE_MOZ_OPENPAGES_TEMP NS_LITERAL_CSTRING( \
   "CREATE TEMP TABLE moz_openpages_temp (" \
-    "  url TEXT" \
-    ", userContextId INTEGER" \
+    "  url TEXT PRIMARY KEY" \
     ", open_count INTEGER" \
-    ", PRIMARY KEY (url, userContextId)" \
   ")" \
 )
 
diff --git a/toolkit/components/places/nsPlacesTriggers.h b/toolkit/components/places/nsPlacesTriggers.h
index d5b45ff5e..37871a3eb 100644
--- a/toolkit/components/places/nsPlacesTriggers.h
+++ b/toolkit/components/places/nsPlacesTriggers.h
@@ -192,8 +192,7 @@
   "WHEN NEW.open_count = 0 " \
   "BEGIN " \
     "DELETE FROM moz_openpages_temp " \
-    "WHERE url = NEW.url " \
-      "AND userContextId = NEW.userContextId;" \
+    "WHERE url = NEW.url;" \
   "END" \
 )
 
diff --git a/toolkit/components/places/tests/unifiedcomplete/head_autocomplete.js b/toolkit/components/places/tests/unifiedcomplete/head_autocomplete.js
index 11e917e18..bc252efe0 100644
--- a/toolkit/components/places/tests/unifiedcomplete/head_autocomplete.js
+++ b/toolkit/components/places/tests/unifiedcomplete/head_autocomplete.js
@@ -286,19 +286,19 @@ var addBookmark = Task.async(function* (aBookmarkObj) {
   }
 });
 
-function addOpenPages(aUri, aCount=1, aUserContextId=0) {
+function addOpenPages(aUri, aCount=1) {
   let ac = Cc["@mozilla.org/autocomplete/search;1?name=unifiedcomplete"]
              .getService(Ci.mozIPlacesAutoComplete);
   for (let i = 0; i < aCount; i++) {
-    ac.registerOpenPage(aUri, aUserContextId);
+    ac.registerOpenPage(aUri);
   }
 }
 
-function removeOpenPages(aUri, aCount=1, aUserContextId=0) {
+function removeOpenPages(aUri, aCount=1) {
   let ac = Cc["@mozilla.org/autocomplete/search;1?name=unifiedcomplete"]
              .getService(Ci.mozIPlacesAutoComplete);
   for (let i = 0; i < aCount; i++) {
-    ac.unregisterOpenPage(aUri, aUserContextId);
+    ac.unregisterOpenPage(aUri);
   }
 }
 
diff --git a/toolkit/components/places/tests/unifiedcomplete/test_tab_matches.js b/toolkit/components/places/tests/unifiedcomplete/test_tab_matches.js
index 740b8d8ed..646519c32 100644
--- a/toolkit/components/places/tests/unifiedcomplete/test_tab_matches.js
+++ b/toolkit/components/places/tests/unifiedcomplete/test_tab_matches.js
@@ -11,11 +11,9 @@ add_task(function* test_tab_matches() {
   let uri2 = NetUtil.newURI("http://xyz.net/");
   let uri3 = NetUtil.newURI("about:mozilla");
   let uri4 = NetUtil.newURI("data:text/html,test");
-  let uri5 = NetUtil.newURI("http://foobar.org");
   yield PlacesTestUtils.addVisits([
     { uri: uri1, title: "ABC rocks" },
-    { uri: uri2, title: "xyz.net - we're better than ABC" },
-    { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ" }
+    { uri: uri2, title: "xyz.net - we're better than ABC" }
   ]);
   addOpenPages(uri1, 1);
   // Pages that cannot be registered in history.
@@ -37,8 +35,7 @@ add_task(function* test_tab_matches() {
     searchParam: "enable-actions",
     matches: [ makeSearchMatch("abc", { heuristic: true }),
                makeSwitchToTabMatch("http://abc.com/", { title: "ABC rocks" }),
-               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] },
-               { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ", style: [ "favicon" ] } ]
+               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] } ]
   });
 
   do_print("three results, both normal results are tab matches");
@@ -48,39 +45,7 @@ add_task(function* test_tab_matches() {
     searchParam: "enable-actions",
     matches: [ makeSearchMatch("abc", { heuristic: true }),
                makeSwitchToTabMatch("http://abc.com/", { title: "ABC rocks" }),
-               makeSwitchToTabMatch("http://xyz.net/", { title: "xyz.net - we're better than ABC" }),
-               { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ", style: [ "favicon" ] } ]
-  });
-
-  do_print("a container tab is not visible in 'switch to tab'");
-  addOpenPages(uri5, 1, /* userContextId: */ 3);
-  yield check_autocomplete({
-    search: "abc",
-    searchParam: "enable-actions",
-    matches: [ makeSearchMatch("abc", { heuristic: true }),
-               makeSwitchToTabMatch("http://abc.com/", { title: "ABC rocks" }),
-               makeSwitchToTabMatch("http://xyz.net/", { title: "xyz.net - we're better than ABC" }),
-               { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ", style: [ "favicon" ] } ]
-  });
-
-  do_print("a container tab should not see 'switch to tab' for other container tabs");
-  yield check_autocomplete({
-    search: "abc",
-    searchParam: "enable-actions user-context-id:3",
-    matches: [ makeSearchMatch("abc", { heuristic: true }),
-               makeSwitchToTabMatch("http://foobar.org/", { title: "foobar.org - much better than ABC, definitely better than XYZ" }),
-               { uri: uri1, title: "ABC rocks", style: [ "favicon" ] },
-               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] } ]
-  });
-
-  do_print("a different container tab should not see any 'switch to tab'");
-  yield check_autocomplete({
-    search: "abc",
-    searchParam: "enable-actions user-context-id:2",
-    matches: [ makeSearchMatch("abc", { heuristic: true }),
-               { uri: uri1, title: "ABC rocks", style: [ "favicon" ] },
-               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] },
-               { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ", style: [ "favicon" ] } ]
+               makeSwitchToTabMatch("http://xyz.net/", { title: "xyz.net - we're better than ABC" }) ]
   });
 
   do_print("three results, both normal results are tab matches, one has multiple tabs");
@@ -90,8 +55,7 @@ add_task(function* test_tab_matches() {
     searchParam: "enable-actions",
     matches: [ makeSearchMatch("abc", { heuristic: true }),
                makeSwitchToTabMatch("http://abc.com/", { title: "ABC rocks" }),
-               makeSwitchToTabMatch("http://xyz.net/", { title: "xyz.net - we're better than ABC" }),
-               { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ", style: [ "favicon" ] } ]
+               makeSwitchToTabMatch("http://xyz.net/", { title: "xyz.net - we're better than ABC" }) ]
   });
 
   do_print("three results, no tab matches (disable-private-actions)");
@@ -100,8 +64,7 @@ add_task(function* test_tab_matches() {
     searchParam: "enable-actions disable-private-actions",
     matches: [ makeSearchMatch("abc", { heuristic: true }),
                { uri: uri1, title: "ABC rocks", style: [ "favicon" ] },
-               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] },
-               { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ", style: [ "favicon" ] } ]
+               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] } ]
   });
 
   do_print("two results (actions disabled)");
@@ -109,8 +72,7 @@ add_task(function* test_tab_matches() {
     search: "abc",
     searchParam: "",
     matches: [ { uri: uri1, title: "ABC rocks", style: [ "favicon" ] },
-               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] },
-               { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ", style: [ "favicon" ] } ]
+               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] } ]
   });
 
   do_print("three results, no tab matches");
@@ -121,8 +83,7 @@ add_task(function* test_tab_matches() {
     searchParam: "enable-actions",
     matches: [ makeSearchMatch("abc", { heuristic: true }),
                { uri: uri1, title: "ABC rocks", style: [ "favicon" ] },
-               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] },
-               { uri: uri5, title: "foobar.org - much better than ABC, definitely better than XYZ", style: [ "favicon" ] } ]
+               { uri: uri2, title: "xyz.net - we're better than ABC", style: [ "favicon" ] } ]
   });
 
   do_print("tab match search with restriction character");
diff --git a/toolkit/components/thumbnails/BackgroundPageThumbs.jsm b/toolkit/components/thumbnails/BackgroundPageThumbs.jsm
index 3ba0c346c..3ed32665d 100644
--- a/toolkit/components/thumbnails/BackgroundPageThumbs.jsm
+++ b/toolkit/components/thumbnails/BackgroundPageThumbs.jsm
@@ -15,8 +15,6 @@ const TELEMETRY_HISTOGRAM_ID_PREFIX = "FX_THUMBNAILS_BG_";
 const XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
 const HTML_NS = "http://www.w3.org/1999/xhtml";
 
-const ABOUT_NEWTAB_SEGREGATION_PREF = "privacy.usercontext.about_newtab_segregation.enabled";
-
 const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
 
 Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
@@ -37,8 +35,6 @@ XPCOMUtils.defineConstant(this, "TEL_CAPTURE_DONE_TIMEOUT", TEL_CAPTURE_DONE_TIM
 XPCOMUtils.defineConstant(this, "TEL_CAPTURE_DONE_CRASHED", TEL_CAPTURE_DONE_CRASHED);
 XPCOMUtils.defineConstant(this, "TEL_CAPTURE_DONE_BAD_URI", TEL_CAPTURE_DONE_BAD_URI);
 
-XPCOMUtils.defineLazyModuleGetter(this, "ContextualIdentityService",
-                                  "resource://gre/modules/ContextualIdentityService.jsm");
 const global = this;
 
 // contains base64 version of a placeholder thumbnail
@@ -139,14 +135,6 @@ const BackgroundPageThumbs = {
   }),
 
   /**
-   * Tell the service that the thumbnail browser should be recreated at next
-   * call of _ensureBrowser().
-   */
-  renewThumbnailBrowser: function() {
-    this._renewThumbBrowser = true;
-  },
-
-  /**
    * Ensures that initialization of the thumbnail browser's parent window has
    * begun.
    *
@@ -201,12 +189,9 @@ const BackgroundPageThumbs = {
    * Creates the thumbnail browser if it doesn't already exist.
    */
   _ensureBrowser: function () {
-    if (this._thumbBrowser && !this._renewThumbBrowser)
+    if (this._thumbBrowser)
       return;
 
-    this._destroyBrowser();
-    this._renewThumbBrowser = false;
-
     let browser = this._parentWin.document.createElementNS(XUL_NS, "browser");
     browser.setAttribute("type", "content");
     browser.setAttribute("disableglobalhistory", "true");
@@ -216,13 +201,6 @@ const BackgroundPageThumbs = {
       browser.setAttribute("remote", "true");
     }
 
-    if (Services.prefs.getBoolPref(ABOUT_NEWTAB_SEGREGATION_PREF)) {
-      // Use the private container for thumbnails.
-      let privateIdentity =
-        ContextualIdentityService.getPrivateIdentity("userContextIdInternal.thumbnail");
-      browser.setAttribute("usercontextid", privateIdentity.userContextId);
-    }
-
     // Size the browser.  Make its aspect ratio the same as the canvases' that
     // the thumbnails are drawn into; the canvases' aspect ratio is the same as
     // the screen's, so use that.  Aim for a size in the ballpark of 1024x768.
@@ -325,14 +303,6 @@ const BackgroundPageThumbs = {
   _destroyBrowserTimeout: DESTROY_BROWSER_TIMEOUT,
 };
 
-Services.prefs.addObserver(ABOUT_NEWTAB_SEGREGATION_PREF,
-  function(aSubject, aTopic, aData) {
-    if (aTopic == "nsPref:changed" && aData == ABOUT_NEWTAB_SEGREGATION_PREF) {
-      BackgroundPageThumbs.renewThumbnailBrowser();
-    }
-  },
-  false);
-
 Object.defineProperty(this, "BackgroundPageThumbs", {
   value: BackgroundPageThumbs,
   enumerable: true,
@@ -467,14 +437,6 @@ Capture.prototype = {
           Cu.reportError(err);
         }
       }
-
-      if (Services.prefs.getBoolPref(ABOUT_NEWTAB_SEGREGATION_PREF)) {
-        // Clear the data in the private container for thumbnails.
-        let privateIdentity =
-          ContextualIdentityService.getPrivateIdentity("userContextIdInternal.thumbnail");
-        Services.obs.notifyObservers(null, "clear-origin-attributes-data",
-          JSON.stringify({ userContextId: privateIdentity.userContextId }));
-      }
     };
 
     if (!data) {