Adding upstream version 127.0.upstream/127.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

66 files changed, 2831 insertions, 2101 deletions

diff --git a/browser/base/content/appmenu-viewcache.inc.xhtml b/browser/base/content/appmenu-viewcache.inc.xhtml
index 6d838bd9d6..9633c7d79d 100644
--- a/browser/base/content/appmenu-viewcache.inc.xhtml
+++ b/browser/base/content/appmenu-viewcache.inc.xhtml
@@ -3,14 +3,11 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 <html:template id="appMenu-viewCache">
-  <!-- This is a placeholder app menu which should be replaced with the "real"
-       Proton app menu before the Proton pref starts getting enabled. -->
-  <panelview id="appMenu-protonMainView" class="PanelUI-subView"
+  <panelview id="appMenu-mainView" class="PanelUI-subView"
              lockpanelvertical="true">
     <vbox class="panel-subview-body">
-      <vbox id="appMenu-proton-addon-banners"/>
-      <toolbarbutton id="appMenu-proton-update-banner" class="panel-banner-item subviewbutton"
-                     oncommand="PanelUI._onBannerItemSelected(event)"
+      <vbox id="appMenu-addon-banners"/>
+      <toolbarbutton id="appMenu-update-banner" class="panel-banner-item subviewbutton"
                      wrap="true"
                      hidden="true"/>
       <toolbaritem id="appMenu-fxa-status2"
@@ -19,7 +16,7 @@
         <html:div id="appMenu-fxa-text" data-l10n-id="appmenu-fxa-sync-and-save-data2"/>
         <toolbarbutton id="appMenu-fxa-label2"
                       class="subviewbutton"
-                      oncommand="gSync.toggleAccountPanel(this, event)">
+                      >
           <vbox flex="1">
             <label id="appMenu-header-title"
                    crop="end"/>
@@ -33,7 +30,6 @@
                      data-l10n-id="appmenuitem-profiles"
                      data-l10n-args='{ "profilename": "" }'
                      closemenu="none"
-                     oncommand="gProfiles.updateView(this)"
                      hidden="true"/>
       <toolbarseparator id="appMenu-fxa-separator" class="proton-zap"/>
       <toolbarbutton id="appMenu-new-tab-button2"
@@ -56,12 +52,12 @@
                      class="subviewbutton subviewbutton-nav"
                      data-l10n-id="library-bookmarks-menu"
                      closemenu="none"
-                     oncommand="BookmarkingUI.showSubView(this);"/>
+                     />
       <toolbarbutton id="appMenu-history-button"
                      class="subviewbutton subviewbutton-nav"
                      data-l10n-id="appmenuitem-history"
                      closemenu="none"
-                     oncommand="PanelUI.showSubView('PanelUI-history', this)"/>
+                     />
       <toolbarbutton id="appMenu-downloads-button"
                      class="subviewbutton"
                      data-l10n-id="appmenuitem-downloads"
@@ -70,7 +66,6 @@
       <toolbarbutton id="appMenu-passwords-button"
                      class="subviewbutton"
                      data-l10n-id="appmenuitem-passwords"
-                     oncommand="LoginHelper.openPasswordManager(window, { entryPoint: 'mainmenu' })"
                      />
       <toolbarbutton id="appMenu-extensions-themes-button"
                      class="subviewbutton"
@@ -119,13 +114,6 @@
                        class="subviewbutton subviewbutton-iconic"
                        data-l10n-id="appmenuitem-fullscreen"
                        type="checkbox"
-# Note that we're custom-handling this click to make sure the panel disappears
-# before entering fullscreen, as it does some odd moving about on the screen
-# in the middle of the fullscreen transition otherwise.
-                       oncommand="
-                         this.closest('panel').hidePopup();
-                         setTimeout(() => BrowserCommands.fullScreen(), 0);
-                       "
                        tooltip="dynamic-shortcut-tooltip">
            <observes element="View:FullScreen" attribute="checked"/>
         </toolbarbutton>
@@ -137,12 +125,12 @@
 #ifdef XP_MACOSX
                      key="key_preferencesCmdMac"
 #endif
-                     oncommand="openPreferences()"/>
+                     />
       <toolbarbutton id="appMenu-more-button2"
                      class="subviewbutton subviewbutton-nav"
                      data-l10n-id="appmenuitem-more-tools"
                      closemenu="none"
-                     oncommand="PanelUI.showMoreToolsPanel(this);"/>
+                     />
       <toolbarbutton id="appMenu-report-broken-site-button"
                      class="subviewbutton subviewbutton-nav"
                      data-l10n-id="appmenuitem-report-broken-site"
@@ -153,7 +141,7 @@
                      class="subviewbutton subviewbutton-nav"
                      data-l10n-id="appmenuitem-help"
                      closemenu="none"
-                     oncommand="PanelUI.showSubView('PanelUI-helpView', this)"/>
+                     />
 #ifndef XP_MACOSX
       <toolbarseparator/>
       <toolbarbutton id="appMenu-quit-button2"
@@ -171,16 +159,16 @@
                      data-l10n-id="appmenu-recently-closed-tabs"
                      class="subviewbutton subviewbutton-nav"
                      closemenu="none"
-                     oncommand="PanelUI.showSubView('appMenu-library-recentlyClosedTabs', this)"/>
+                     />
       <toolbarbutton id="appMenuRecentlyClosedWindows"
                      data-l10n-id="appmenu-recently-closed-windows"
                      class="subviewbutton subviewbutton-nav"
                      closemenu="none"
-                     oncommand="PanelUI.showSubView('appMenu-library-recentlyClosedWindows', this)"/>
+                     />
       <toolbarbutton id="appMenuSearchHistory"
                      data-l10n-id="appmenu-search-history"
                      class="subviewbutton"
-                     oncommand="PlacesCommandHook.searchHistory()"/>
+                     />
       <toolbarbutton id="appMenu-restoreSession"
                      data-l10n-id="appmenu-restore-session"
                      class="subviewbutton"
@@ -206,7 +194,7 @@
     <toolbarbutton id="PanelUI-historyMore"
                    class="subviewbutton panel-subview-footer-button"
                    data-l10n-id="appmenu-manage-history"
-                   oncommand="PlacesCommandHook.showPlacesOrganizer('History'); CustomizableUI.hidePanelForNode(this);"/>
+                   />
   </panelview>
 
   <panelview id="PanelUI-profiles" flex="1">
@@ -217,10 +205,10 @@
         <hbox id="this-profile-buttons">
           <toolbarbutton id="profiles-edit-this-delete-button"
                          class="subviewbutton toolbarbutton-1"
-                         oncommand="switchToTabHavingURI('about:profilemanager', true)"/>
+                         />
           <toolbarbutton id="profiles-delete-this-profile-button"
                          class="subviewbutton toolbarbutton-1"
-                         oncommand="switchToTabHavingURI('about:profilemanager', true)"/>
+                         />
         </hbox>
       </vbox>
       <toolbarseparator/>
@@ -230,15 +218,15 @@
                      class="subviewbutton"
                      data-l10n-id="appmenu-close-profile"
                      data-l10n-args='{ "profilename": "" }'
-                     oncommand=""/>
+                     />
       <toolbarbutton id="profiles-create-profile-button"
                      class="subviewbutton"
                      data-l10n-id="appmenu-create-profile"
-                     oncommand="switchToTabHavingURI('about:profilemanager', true)"/>
+                     />
       <toolbarbutton id="profiles-manage-profiles-button"
                      class="subviewbutton"
                      data-l10n-id="appmenu-manage-profiles"
-                     oncommand="switchToTabHavingURI('about:profilemanager', true)"/>
+                     />
     </vbox>
   </panelview>
 
@@ -262,12 +250,12 @@
       <toolbarbutton id="panelMenu_searchBookmarks"
                      data-l10n-id="bookmarks-search"
                      class="subviewbutton"
-                     oncommand="PlacesCommandHook.searchBookmarks();"/>
+                     />
       <toolbarbutton id="panelMenu_viewBookmarksToolbar"
                      class="subviewbutton"
                      data-l10n-id="bookmarks-tools-toolbar-visibility-panel"
                      data-l10n-args='{ "isVisible": false }'
-                     oncommand="BookmarkingUI.toggleBookmarksToolbar('bookmark-tools');"/>
+                     />
       <toolbarseparator/>
       <html:h2 id="panelMenu_recentBookmarks"
           data-l10n-id="bookmarks-recent-bookmarks-panel-subheader"
@@ -460,8 +448,6 @@
           <toolbarbutton id="PanelUI-remotetabs-syncnow"
                          align="center"
                          class="subviewbutton"
-                         oncommand="gSync.doSync();"
-                         onmouseover="gSync.refreshSyncButtonsTooltip();"
                          closemenu="none">
             <hbox flex="1">
               <image class="syncNowBtn"/>
@@ -476,7 +462,7 @@
           <toolbarbutton id="PanelUI-remotetabs-view-managedevices"
                          class="subviewbutton"
                          data-l10n-id="appmenuitem-fxa-manage-account"
-                         oncommand="gSync.openDevicesManagementPage('syncedtabs-menupanel');">
+                         >
                          <observes element="sidebar-box" attribute="positionend"/>
           </toolbarbutton>
           <toolbarseparator id="PanelUI-remotetabs-separator"/>
@@ -503,7 +489,7 @@
                 <toolbarbutton class="PanelUI-remotetabs-button"
                                id="PanelUI-remotetabs-tabsdisabledpane-button"
                                data-l10n-id="appmenu-remote-tabs-opensettings"
-                               oncommand="gSync.openPrefs('synced-tabs');"/>
+                               />
               </hbox>
             </vbox>
           </hbox>
@@ -517,7 +503,7 @@
               <toolbarbutton id="PanelUI-remotetabs-connect-device-button"
                              class="PanelUI-remotetabs-button"
                              data-l10n-id="appmenu-remote-tabs-connectdevice"
-                             oncommand="gSync.openConnectAnotherDevice('synced-tabs');"/>
+                             />
             </vbox>
           </hbox>
         </deck>
@@ -535,7 +521,7 @@
           <toolbarbutton class="PanelUI-remotetabs-button"
                          id="PanelUI-remotetabs-setupsync-button"
                          data-l10n-id="appmenu-remote-tabs-sign-into-sync"
-                         oncommand="gSync.openPrefs('synced-tabs');"/>
+                         />
         </vbox>
         <!-- When Sync is not enabled -->
         <vbox id="PanelUI-remotetabs-syncdisabled"
@@ -548,7 +534,7 @@
           <toolbarbutton class="PanelUI-remotetabs-button"
                          id="PanelUI-remotetabs-syncdisabled-button"
                          data-l10n-id="appmenu-remote-tabs-turn-on-sync"
-                         oncommand="gSync.openPrefs('synced-tabs');"/>
+                         />
         </vbox>
         <!-- When Sync needs re-authentication -->
         <vbox id="PanelUI-remotetabs-reauthsync"
@@ -561,7 +547,7 @@
           <toolbarbutton class="PanelUI-remotetabs-button"
                          id="PanelUI-remotetabs-reauthsync-button"
                          data-l10n-id="appmenu-remote-tabs-sign-into-sync"
-                         oncommand="gSync.openPrefs('synced-tabs');"/>
+                         />
         </vbox>
         <!-- When Sync needs verification -->
         <vbox id="PanelUI-remotetabs-unverified"
@@ -574,7 +560,7 @@
           <toolbarbutton class="PanelUI-remotetabs-button"
                          id="PanelUI-remotetabs-unverified-button"
                          data-l10n-id="appmenu-remote-tabs-opensettings"
-                         oncommand="gSync.openPrefs('synced-tabs');"/>
+                         />
         </vbox>
       </hbox>
     </vbox>
@@ -585,7 +571,7 @@
       <toolbarbutton id="fxa-manage-account-button"
                      align="center"
                      class="subviewbutton"
-                     oncommand="gSync.clickFxAMenuHeaderButton(this);">
+                     >
         <vbox flex="1">
           <label id="fxa-menu-header-title"
                  crop="end"
@@ -599,8 +585,6 @@
       <toolbarbutton id="PanelUI-fxa-menu-syncnow-button"
                      align="center"
                      class="subviewbutton"
-                     oncommand="gSync.doSyncFromFxaMenu(this);"
-                     onmouseover="gSync.refreshSyncButtonsTooltip();"
                      closemenu="none">
         <hbox flex="1">
           <image id="PanelUI-appMenu-fxa-image-last-synced"
@@ -617,43 +601,34 @@
       <toolbarbutton id="PanelUI-fxa-menu-setup-sync-button"
                       class="subviewbutton"
                       data-l10n-id="appmenu-fxa-setup-sync"
-                      oncommand="gSync.openPrefsFromFxaMenu('sync_settings', this);"/>
+                      />
       <!-- The `Connect Another Device` button is disabled by default until the user logs into Sync. -->
       <toolbarbutton id="PanelUI-fxa-menu-connect-device-button"
                       class="subviewbutton"
                       data-l10n-id="fxa-menu-connect-another-device"
                       disabled="true"
-                      oncommand="gSync.openConnectAnotherDeviceFromFxaMenu(this);"/>
+                      />
       <toolbarbutton id="PanelUI-fxa-menu-sendtab-button"
                       class="subviewbutton subviewbutton-nav"
                       data-l10n-id="fxa-menu-send-tab-to-device"
                       data-l10n-args='{"tabCount":1}'
                       closemenu="none"
-                      oncommand="gSync.showSendToDeviceViewFromFxaMenu(this);"/>
+                      />
       <toolbarbutton id="PanelUI-fxa-menu-sync-prefs-button"
                       class="subviewbutton"
                       data-l10n-id="fxa-menu-sync-settings"
                       hidden="true"
-                      oncommand="gSync.openPrefsFromFxaMenu('sync_settings', this);"/>
+                      />
       <toolbarseparator id="PanelUI-sign-out-separator" />
       <toolbarbutton id="PanelUI-fxa-menu-account-signout-button"
               class="subviewbutton"
               data-l10n-id="fxa-menu-sign-out"
-              oncommand="gSync.disconnect();"
               hidden="true"/>
       </vbox>
       <!-- updateCTAPanel will control if we show this panel -->
-      <vbox id="PanelUI-fxa-cta-menu">
-        <toolbarbutton id="PanelUI-fxa-menu-sync-button" class="subviewbutton subviewbutton-iconic"
-          oncommand="gSync.openPrefsFromFxaButton('sync_cta', this);">
-          <vbox flex="1">
-            <label id="fxa-menu-header-title" crop="end" data-l10n-id="fxa-menu-sync-title" />
-            <label id="cta-menu-header-description" crop="end" data-l10n-id="fxa-menu-sync-description" />
-          </vbox>
-        </toolbarbutton>
+      <vbox id="PanelUI-fxa-cta-menu" hidden="true">
         <toolbarseparator id="PanelUI-products-separator" />
-        <toolbarbutton id="PanelUI-fxa-menu-monitor-button" class="subviewbutton subviewbutton-iconic"
-          oncommand="gSync.openMonitorLink(this)">
+        <toolbarbutton id="PanelUI-fxa-menu-monitor-button" class="fxa-cta-button subviewbutton subviewbutton-iconic">
           <vbox flex="1">
             <hbox align="center">
               <image class="PanelUI-fxa-menu-monitor-button ctaMenuLogo" role="presentation" />
@@ -662,8 +637,7 @@
             <label id="cta-menu-header-description" crop="end" data-l10n-id="appmenuitem-monitor-description" />
           </vbox>
         </toolbarbutton>
-        <toolbarbutton id="PanelUI-fxa-menu-relay-button" class="subviewbutton subviewbutton-iconic"
-          oncommand="gSync.openRelayLink(this)">
+        <toolbarbutton id="PanelUI-fxa-menu-relay-button" class="fxa-cta-button subviewbutton subviewbutton-iconic">
           <vbox flex="1">
             <hbox align="center">
               <image class="PanelUI-fxa-menu-relay-button ctaMenuLogo" role="presentation" />
@@ -672,8 +646,7 @@
             <label id="cta-menu-header-description" crop="end" data-l10n-id="appmenuitem-relay-description" />
           </vbox>
         </toolbarbutton>
-        <toolbarbutton id="PanelUI-fxa-menu-vpn-button" class="subviewbutton subviewbutton-iconic"
-          oncommand="gSync.openVPNLink(this)">
+        <toolbarbutton id="PanelUI-fxa-menu-vpn-button" class="fxa-cta-button subviewbutton subviewbutton-iconic">
           <vbox flex="1">
             <hbox align="center">
               <image class="PanelUI-fxa-menu-vpn-button ctaMenuLogo" role="presentation" />
@@ -715,7 +688,7 @@
       <toolbarbutton id="PanelUI-fxa-menu-sendtab-not-configured-button"
                      class="PanelUI-fxa-signin-button"
                      data-l10n-id="appmenuitem-fxa-sign-in"
-                     oncommand="gSync.openPrefsFromFxaMenu('send_tab', this);"/>
+                     />
     </vbox>
   </panelview>
 
@@ -726,7 +699,15 @@
       <toolbarbutton id="PanelUI-fxa-menu-sendtab-connect-device-button"
                      class="PanelUI-fxa-signin-button"
                      data-l10n-id="appmenu-remote-tabs-connectdevice"
-                     oncommand="gSync.openConnectAnotherDeviceFromFxaMenu(this);"/>
+                     />
+    </vbox>
+  </panelview>
+
+  <!-- This panelview holds the list of "inactive" tabs for devices -->
+  <panelview id="PanelUI-fxa-menu-inactive-tabs" class="PanelUI-subView PanelUI-remotetabs-clientcontainer">
+    <label itemtype="client">
+    </label>
+    <vbox class="panel-subview-body">
     </vbox>
   </panelview>
 
@@ -736,16 +717,16 @@
                      class="subviewbutton subviewbutton-nav"
                      data-l10n-id="library-bookmarks-menu"
                      closemenu="none"
-                     oncommand="BookmarkingUI.showSubView(this);"/>
+                     />
       <toolbarbutton id="appMenu-library-history-button"
                      class="subviewbutton subviewbutton-nav"
                      data-l10n-id="appmenuitem-history"
                      closemenu="none"
-                     oncommand="PanelUI.showSubView('PanelUI-history', this)"/>
+                     />
       <toolbarbutton id="appMenu-library-downloads-button"
                      class="subviewbutton"
                      data-l10n-id="appmenuitem-downloads"
-                     oncommand="DownloadsPanel.showDownloadsHistory();"/>
+                     />
     </vbox>
   </panelview>
 
@@ -762,15 +743,29 @@
         <button id="reset-pbm-panel-cancel-button"
                 class="footer-button"
                 data-l10n-id="reset-pbm-panel-cancel-button"
-                oncommand="ResetPBMPanel.onCancel(this)"></button>
+                ></button>
         <button slot="primary"
                 id="reset-pbm-panel-confirm-button"
                 class="footer-button"
                 data-l10n-id="reset-pbm-panel-confirm-button"
-                oncommand="ResetPBMPanel.onConfirm(this)"></button>
+                ></button>
       </html:moz-button-group>
     </vbox>
   </panelview>
 
+  <panelview id="content-analysis-panel" class="PanelUI-subView" role="document" mainview-with-header="true">
+    <vbox id="content-analysis-panel-container" role="alertdialog" aria-labelledby="content-analysis-header">
+      <hbox class="panel-header">
+        <html:h1 id="content-analysis-header" data-l10n-id="content-analysis-panel-title"/>
+      </hbox>
+      <description id="content-analysis-panel-description">
+        <html:a is="moz-support-link"
+                data-l10n-name="info"
+                class="learnMore"
+                support-page="data-loss-prevention"/>
+      </description>
+    </vbox>
+  </panelview>
+
 #include ../../components/reportbrokensite/content/reportBrokenSitePanel.inc.xhtml
 </html:template>
diff --git a/browser/base/content/browser-addons.js b/browser/base/content/browser-addons.js
index 1e97428e24..e00952b2dc 100644
--- a/browser/base/content/browser-addons.js
+++ b/browser/base/content/browser-addons.js
@@ -618,7 +618,6 @@ var gXPInstallObserver = {
         break;
       }
       case "addon-install-blocked": {
-        await window.ensureCustomElements("moz-support-link");
         // Dismiss the progress notification.  Note that this is bad if
         // there are multiple simultaneous installs happening, see
         // bug 1329884 for a longer explanation.
@@ -1089,27 +1088,18 @@ var BrowserAddonUI = {
     return { remove: result === 0, report: checkboxState.value };
   },
 
-  async reportAddon(addonId, reportEntryPoint) {
+  async reportAddon(addonId, _reportEntryPoint) {
     let addon = addonId && (await AddonManager.getAddonByID(addonId));
     if (!addon) {
       return;
     }
 
-    // Do not open an additional about:addons tab if the abuse report should be
-    // opened in its own tab.
-    if (lazy.AbuseReporter.amoFormEnabled) {
-      const amoUrl = lazy.AbuseReporter.getAMOFormURL({ addonId });
-      window.openTrustedLinkIn(amoUrl, "tab", {
-        // Make sure the newly open tab is going to be focused, independently
-        // from general user prefs.
-        forceForeground: true,
-      });
-      return;
-    }
-
-    const win = await BrowserOpenAddonsMgr("addons://list/extension");
-
-    win.openAbuseReport({ addonId, reportEntryPoint });
+    const amoUrl = lazy.AbuseReporter.getAMOFormURL({ addonId });
+    window.openTrustedLinkIn(amoUrl, "tab", {
+      // Make sure the newly open tab is going to be focused, independently
+      // from general user prefs.
+      forceForeground: true,
+    });
   },
 
   async removeAddon(addonId) {
@@ -1137,7 +1127,85 @@ var BrowserAddonUI = {
       return;
     }
 
-    BrowserOpenAddonsMgr("addons://detail/" + encodeURIComponent(addon.id));
+    this.openAddonsMgr("addons://detail/" + encodeURIComponent(addon.id));
+  },
+
+  /**
+   * Open about:addons page by given view id.
+   * @param {String} aView
+   *                 View id of page that will open.
+   *                 e.g. "addons://discover/"
+   * @param {Object} options
+   *        {
+   *          selectTabByViewId: If true, if there is the tab opening page having
+   *                             same view id, select the tab. Else if the current
+   *                             page is blank, load on it. Otherwise, open a new
+   *                             tab, then load on it.
+   *                             If false, if there is the tab opening
+   *                             about:addoons page, select the tab and load page
+   *                             for view id on it. Otherwise, leave the loading
+   *                             behavior to switchToTabHavingURI().
+   *                             If no options, handles as false.
+   *        }
+   * @returns {Promise} When the Promise resolves, returns window object loaded the
+   *                    view id.
+   */
+  openAddonsMgr(aView, { selectTabByViewId = false } = {}) {
+    return new Promise(resolve => {
+      let emWindow;
+      let browserWindow;
+
+      const receivePong = function (aSubject) {
+        const browserWin = aSubject.browsingContext.topChromeWindow;
+        if (!emWindow || browserWin == window /* favor the current window */) {
+          if (
+            selectTabByViewId &&
+            aSubject.gViewController.currentViewId !== aView
+          ) {
+            return;
+          }
+
+          emWindow = aSubject;
+          browserWindow = browserWin;
+        }
+      };
+      Services.obs.addObserver(receivePong, "EM-pong");
+      Services.obs.notifyObservers(null, "EM-ping");
+      Services.obs.removeObserver(receivePong, "EM-pong");
+
+      if (emWindow) {
+        if (aView && !selectTabByViewId) {
+          emWindow.loadView(aView);
+        }
+        let tab = browserWindow.gBrowser.getTabForBrowser(
+          emWindow.docShell.chromeEventHandler
+        );
+        browserWindow.gBrowser.selectedTab = tab;
+        emWindow.focus();
+        resolve(emWindow);
+        return;
+      }
+
+      if (selectTabByViewId) {
+        const target = isBlankPageURL(gBrowser.currentURI.spec)
+          ? "current"
+          : "tab";
+        openTrustedLinkIn("about:addons", target);
+      } else {
+        // This must be a new load, else the ping/pong would have
+        // found the window above.
+        switchToTabHavingURI("about:addons", true);
+      }
+
+      Services.obs.addObserver(function observer(aSubject, aTopic) {
+        Services.obs.removeObserver(observer, aTopic);
+        if (aView) {
+          aSubject.loadView(aView);
+        }
+        aSubject.focus();
+        resolve(aSubject);
+      }, "EM-loaded");
+    });
   },
 };
 
@@ -1551,7 +1619,7 @@ var gUnifiedExtensions = {
           } else {
             viewID = "addons://list/extension";
           }
-          await BrowserOpenAddonsMgr(viewID);
+          await BrowserAddonUI.openAddonsMgr(viewID);
           return;
         }
       }
@@ -1877,8 +1945,6 @@ var gUnifiedExtensions = {
     supportPage = null,
     type = "warning",
   }) {
-    window.ensureCustomElements("moz-message-bar");
-
     const messageBar = document.createElement("moz-message-bar");
     messageBar.setAttribute("type", type);
     messageBar.classList.add("unified-extensions-message-bar");
@@ -1886,8 +1952,6 @@ var gUnifiedExtensions = {
     messageBar.setAttribute("data-l10n-attrs", "heading, message");
 
     if (supportPage) {
-      window.ensureCustomElements("moz-support-link");
-
       const supportUrl = document.createElement("a", {
         is: "moz-support-link",
       });
diff --git a/browser/base/content/browser-allTabsMenu.inc.xhtml b/browser/base/content/browser-allTabsMenu.inc.xhtml
index 71d26288f7..1be6576605 100644
--- a/browser/base/content/browser-allTabsMenu.inc.xhtml
+++ b/browser/base/content/browser-allTabsMenu.inc.xhtml
@@ -9,6 +9,10 @@
                      class="subviewbutton"
                      oncommand="gTabsPanel.searchTabs();"
                      data-l10n-id="all-tabs-menu-search-tabs"/>
+      <toolbarbutton id="allTabsMenu-closeDuplicateTabs"
+                     class="subviewbutton"
+                     oncommand="gBrowser.removeAllDuplicateTabs();"
+                     data-l10n-id="all-tabs-menu-close-duplicate-tabs"/>
       <toolbarbutton id="allTabsMenu-containerTabsButton"
                      class="subviewbutton subviewbutton-nav"
                      closemenu="none"
diff --git a/browser/base/content/browser-allTabsMenu.js b/browser/base/content/browser-allTabsMenu.js
index a9caeffca0..f4b15bc9c3 100644
--- a/browser/base/content/browser-allTabsMenu.js
+++ b/browser/base/content/browser-allTabsMenu.js
@@ -6,6 +6,7 @@
 /* eslint-env mozilla/browser-window */
 
 ChromeUtils.defineESModuleGetters(this, {
+  BrowserUsageTelemetry: "resource:///modules/BrowserUsageTelemetry.sys.mjs",
   TabsPanel: "resource:///modules/TabsList.sys.mjs",
 });
 
@@ -72,6 +73,16 @@ var gTabsPanel = {
         !hasHiddenTabs;
       document.getElementById("allTabsMenu-hiddenTabsSeparator").hidden =
         !hasHiddenTabs;
+
+      let closeDuplicateEnabled = Services.prefs.getBoolPref(
+        "browser.tabs.context.close-duplicate.enabled"
+      );
+      let closeDuplicateTabsItem = document.getElementById(
+        "allTabsMenu-closeDuplicateTabs"
+      );
+      closeDuplicateTabsItem.hidden = !closeDuplicateEnabled;
+      closeDuplicateTabsItem.disabled =
+        !closeDuplicateEnabled || !gBrowser.getAllDuplicateTabsToClose().length;
     });
 
     this.allTabsView.addEventListener("ViewShown", () =>
@@ -149,6 +160,10 @@ var gTabsPanel = {
         entrypoint,
         1
       );
+      BrowserUsageTelemetry.recordInteractionEvent(
+        entrypoint,
+        "all-tabs-panel-entrypoint"
+      );
       PanelUI.showSubView(
         this.kElements.allTabsView,
         this.allTabsButton,
diff --git a/browser/base/content/browser-box.inc.xhtml b/browser/base/content/browser-box.inc.xhtml
index 41258d81bb..b030891144 100644
--- a/browser/base/content/browser-box.inc.xhtml
+++ b/browser/base/content/browser-box.inc.xhtml
@@ -3,7 +3,7 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 <hbox flex="1" id="browser">
-  <html:sidebar-launcher id="sidebar-launcher" flex="1" hidden="true"></html:sidebar-launcher>
+  <html:sidebar-main id="sidebar-main" flex="1" hidden="true"></html:sidebar-main>
   <vbox id="sidebar-box" hidden="true" class="chromeclass-extrachrome">
     <box id="sidebar-header" align="center">
       <toolbarbutton id="sidebar-switcher-target" class="tabbable" aria-expanded="false">
@@ -13,7 +13,7 @@
       </toolbarbutton>
       <image id="sidebar-throbber"/>
       <spacer id="sidebar-spacer"/>
-      <toolbarbutton id="sidebar-close" class="close-icon tabbable" data-l10n-id="sidebar-close-button" oncommand="SidebarUI.hide();"/>
+      <toolbarbutton id="sidebar-close" class="close-icon tabbable" data-l10n-id="sidebar-close-button" oncommand="SidebarController.hide();"/>
     </box>
     <browser id="sidebar" autoscroll="false" disablehistory="true" disablefullscreen="true" tooltip="aHTMLTooltip"/>
   </vbox>
diff --git a/browser/base/content/browser-commands.js b/browser/base/content/browser-commands.js
index 40eb4d5baa..d80f9588cd 100644
--- a/browser/base/content/browser-commands.js
+++ b/browser/base/content/browser-commands.js
@@ -295,7 +295,7 @@ var BrowserCommands = {
     let where = "tab";
 
     if (event) {
-      where = whereToOpenLink(event, false, true);
+      where = BrowserUtils.whereToOpenLink(event, false, true);
 
       switch (where) {
         case "tab":
@@ -573,4 +573,19 @@ var BrowserCommands = {
   fullScreen() {
     window.fullScreen = !window.fullScreen || BrowserHandler.kiosk;
   },
+
+  downloadsUI() {
+    if (PrivateBrowsingUtils.isWindowPrivate(window)) {
+      openTrustedLinkIn("about:downloads", "tab");
+    } else {
+      PlacesCommandHook.showPlacesOrganizer("Downloads");
+    }
+  },
+
+  forceEncodingDetection() {
+    gBrowser.selectedBrowser.forceEncodingDetection();
+    BrowserCommands.reloadWithFlags(
+      Ci.nsIWebNavigation.LOAD_FLAGS_CHARSET_CHANGE
+    );
+  },
 };
diff --git a/browser/base/content/browser-init.js b/browser/base/content/browser-init.js
new file mode 100644
index 0000000000..0717ce2138
--- /dev/null
+++ b/browser/base/content/browser-init.js
@@ -0,0 +1,1107 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+let _resolveDelayedStartup;
+var delayedStartupPromise = new Promise(resolve => {
+  _resolveDelayedStartup = resolve;
+});
+
+var gBrowserInit = {
+  delayedStartupFinished: false,
+  domContentLoaded: false,
+
+  _tabToAdopt: undefined,
+  _firstContentWindowPaintDeferred: Promise.withResolvers(),
+  idleTasksFinished: Promise.withResolvers(),
+
+  _setupFirstContentWindowPaintPromise() {
+    let lastTransactionId = window.windowUtils.lastTransactionId;
+    let layerTreeListener = () => {
+      if (this.getTabToAdopt()) {
+        // Need to wait until we finish adopting the tab, or we might end
+        // up focusing the initial browser and then losing focus when it
+        // gets swapped out for the tab to adopt.
+        return;
+      }
+      removeEventListener("MozLayerTreeReady", layerTreeListener);
+      let listener = e => {
+        if (e.transactionId > lastTransactionId) {
+          window.removeEventListener("MozAfterPaint", listener);
+          this._firstContentWindowPaintDeferred.resolve();
+        }
+      };
+      addEventListener("MozAfterPaint", listener);
+    };
+    addEventListener("MozLayerTreeReady", layerTreeListener);
+  },
+
+  getTabToAdopt() {
+    if (this._tabToAdopt !== undefined) {
+      return this._tabToAdopt;
+    }
+
+    if (window.arguments && window.XULElement.isInstance(window.arguments[0])) {
+      this._tabToAdopt = window.arguments[0];
+
+      // Clear the reference of the tab being adopted from the arguments.
+      window.arguments[0] = null;
+    } else {
+      // There was no tab to adopt in the arguments, set _tabToAdopt to null
+      // to avoid checking it again.
+      this._tabToAdopt = null;
+    }
+
+    return this._tabToAdopt;
+  },
+
+  _clearTabToAdopt() {
+    this._tabToAdopt = null;
+  },
+
+  // Used to check if the new window is still adopting an existing tab as its first tab
+  // (e.g. from the WebExtensions internals).
+  isAdoptingTab() {
+    return !!this.getTabToAdopt();
+  },
+
+  onBeforeInitialXULLayout() {
+    this._setupFirstContentWindowPaintPromise();
+
+    updateBookmarkToolbarVisibility();
+
+    // Set a sane starting width/height for all resolutions on new profiles.
+    if (ChromeUtils.shouldResistFingerprinting("RoundWindowSize", null)) {
+      // When the fingerprinting resistance is enabled, making sure that we don't
+      // have a maximum window to interfere with generating rounded window dimensions.
+      document.documentElement.setAttribute("sizemode", "normal");
+    } else if (!document.documentElement.hasAttribute("width")) {
+      const TARGET_WIDTH = 1280;
+      const TARGET_HEIGHT = 1040;
+      let width = Math.min(screen.availWidth * 0.9, TARGET_WIDTH);
+      let height = Math.min(screen.availHeight * 0.9, TARGET_HEIGHT);
+
+      document.documentElement.setAttribute("width", width);
+      document.documentElement.setAttribute("height", height);
+
+      if (width < TARGET_WIDTH && height < TARGET_HEIGHT) {
+        document.documentElement.setAttribute("sizemode", "maximized");
+      }
+    }
+    if (AppConstants.MENUBAR_CAN_AUTOHIDE) {
+      const toolbarMenubar = document.getElementById("toolbar-menubar");
+      // set a default value
+      if (!toolbarMenubar.hasAttribute("autohide")) {
+        toolbarMenubar.setAttribute("autohide", true);
+      }
+      document.l10n.setAttributes(
+        toolbarMenubar,
+        "toolbar-context-menu-menu-bar-cmd"
+      );
+      toolbarMenubar.setAttribute("data-l10n-attrs", "toolbarname");
+    }
+
+    // Run menubar initialization first, to avoid TabsInTitlebar code picking
+    // up mutations from it and causing a reflow.
+    AutoHideMenubar.init();
+    // Update the chromemargin attribute so the window can be sized correctly.
+    window.TabBarVisibility.update();
+    TabsInTitlebar.init();
+
+    new LightweightThemeConsumer(document);
+
+    if (
+      Services.prefs.getBoolPref(
+        "toolkit.legacyUserProfileCustomizations.windowIcon",
+        false
+      )
+    ) {
+      document.documentElement.setAttribute("icon", "main-window");
+    }
+
+    // Call this after we set attributes that might change toolbars' computed
+    // text color.
+    ToolbarIconColor.init();
+  },
+
+  onDOMContentLoaded() {
+    // This needs setting up before we create the first remote browser.
+    window.docShell.treeOwner
+      .QueryInterface(Ci.nsIInterfaceRequestor)
+      .getInterface(Ci.nsIAppWindow).XULBrowserWindow = window.XULBrowserWindow;
+    window.browserDOMWindow = new nsBrowserAccess();
+
+    gBrowser = window._gBrowser;
+    delete window._gBrowser;
+    gBrowser.init();
+
+    BrowserWindowTracker.track(window);
+
+    FirefoxViewHandler.init();
+
+    gNavToolbox.palette = document.getElementById(
+      "BrowserToolbarPalette"
+    ).content;
+    for (let area of CustomizableUI.areas) {
+      let type = CustomizableUI.getAreaType(area);
+      if (type == CustomizableUI.TYPE_TOOLBAR) {
+        let node = document.getElementById(area);
+        CustomizableUI.registerToolbarNode(node);
+      }
+    }
+    BrowserSearch.initPlaceHolder();
+
+    // Hack to ensure that the various initial pages favicon is loaded
+    // instantaneously, to avoid flickering and improve perceived performance.
+    this._callWithURIToLoad(uriToLoad => {
+      let url;
+      try {
+        url = Services.io.newURI(uriToLoad);
+      } catch (e) {
+        return;
+      }
+      let nonQuery = url.prePath + url.filePath;
+      if (nonQuery in gPageIcons) {
+        gBrowser.setIcon(gBrowser.selectedTab, gPageIcons[nonQuery]);
+      }
+    });
+
+    updateFxaToolbarMenu(gFxaToolbarEnabled, true);
+
+    updatePrintCommands(gPrintEnabled);
+
+    gUnifiedExtensions.init();
+
+    // Setting the focus will cause a style flush, it's preferable to call anything
+    // that will modify the DOM from within this function before this call.
+    this._setInitialFocus();
+
+    this.domContentLoaded = true;
+  },
+
+  onLoad() {
+    gBrowser.addEventListener("DOMUpdateBlockedPopups", gPopupBlockerObserver);
+    gBrowser.addEventListener(
+      "TranslationsParent:LanguageState",
+      FullPageTranslationsPanel
+    );
+    gBrowser.addEventListener(
+      "TranslationsParent:OfferTranslation",
+      FullPageTranslationsPanel
+    );
+    gBrowser.addTabsProgressListener(FullPageTranslationsPanel);
+
+    window.addEventListener("AppCommand", HandleAppCommandEvent, true);
+
+    // These routines add message listeners. They must run before
+    // loading the frame script to ensure that we don't miss any
+    // message sent between when the frame script is loaded and when
+    // the listener is registered.
+    CaptivePortalWatcher.init();
+    ZoomUI.init(window);
+
+    if (!gMultiProcessBrowser) {
+      // There is a Content:Click message manually sent from content.
+      gBrowser.tabpanels.addEventListener("click", contentAreaClick, {
+        capture: true,
+        mozSystemGroup: true,
+      });
+    }
+
+    // hook up UI through progress listener
+    gBrowser.addProgressListener(window.XULBrowserWindow);
+    gBrowser.addTabsProgressListener(window.TabsProgressListener);
+
+    SidebarController.init();
+
+    // We do this in onload because we want to ensure the button's state
+    // doesn't flicker as the window is being shown.
+    DownloadsButton.init();
+
+    // Certain kinds of automigration rely on this notification to complete
+    // their tasks BEFORE the browser window is shown. SessionStore uses it to
+    // restore tabs into windows AFTER important parts like gMultiProcessBrowser
+    // have been initialized.
+    Services.obs.notifyObservers(window, "browser-window-before-show");
+
+    if (!window.toolbar.visible) {
+      // adjust browser UI for popups
+      gURLBar.readOnly = true;
+    }
+
+    // Misc. inits.
+    gUIDensity.init();
+    TabletModeUpdater.init();
+    CombinedStopReload.ensureInitialized();
+    gPrivateBrowsingUI.init();
+    BrowserSearch.init();
+    BrowserPageActions.init();
+    if (gToolbarKeyNavEnabled) {
+      ToolbarKeyboardNavigator.init();
+    }
+
+    // Update UI if browser is under remote control.
+    gRemoteControl.updateVisualCue();
+
+    // If we are given a tab to swap in, take care of it before first paint to
+    // avoid an about:blank flash.
+    let tabToAdopt = this.getTabToAdopt();
+    if (tabToAdopt) {
+      let evt = new CustomEvent("before-initial-tab-adopted", {
+        bubbles: true,
+      });
+      gBrowser.tabpanels.dispatchEvent(evt);
+
+      // Stop the about:blank load
+      gBrowser.stop();
+
+      // Remove the speculative focus from the urlbar to let the url be formatted.
+      gURLBar.removeAttribute("focused");
+
+      let swapBrowsers = () => {
+        try {
+          gBrowser.swapBrowsersAndCloseOther(gBrowser.selectedTab, tabToAdopt);
+        } catch (e) {
+          console.error(e);
+        }
+
+        // Clear the reference to the tab once its adoption has been completed.
+        this._clearTabToAdopt();
+      };
+      if (tabToAdopt.linkedBrowser.isRemoteBrowser) {
+        // For remote browsers, wait for the paint event, otherwise the tabs
+        // are not yet ready and focus gets confused because the browser swaps
+        // out while tabs are switching.
+        addEventListener("MozAfterPaint", swapBrowsers, { once: true });
+      } else {
+        swapBrowsers();
+      }
+    }
+
+    // Wait until chrome is painted before executing code not critical to making the window visible
+    this._boundDelayedStartup = this._delayedStartup.bind(this);
+    window.addEventListener("MozAfterPaint", this._boundDelayedStartup);
+
+    if (!PrivateBrowsingUtils.enabled) {
+      document.getElementById("Tools:PrivateBrowsing").hidden = true;
+      // Setting disabled doesn't disable the shortcut, so we just remove
+      // the keybinding.
+      document.getElementById("key_privatebrowsing").remove();
+    }
+
+    if (BrowserUIUtils.quitShortcutDisabled) {
+      document.getElementById("key_quitApplication").remove();
+      document.getElementById("menu_FileQuitItem").removeAttribute("key");
+
+      PanelMultiView.getViewNode(
+        document,
+        "appMenu-quit-button2"
+      )?.removeAttribute("key");
+    }
+
+    this._loadHandled = true;
+  },
+
+  _cancelDelayedStartup() {
+    window.removeEventListener("MozAfterPaint", this._boundDelayedStartup);
+    this._boundDelayedStartup = null;
+  },
+
+  _delayedStartup() {
+    let { TelemetryTimestamps } = ChromeUtils.importESModule(
+      "resource://gre/modules/TelemetryTimestamps.sys.mjs"
+    );
+    TelemetryTimestamps.add("delayedStartupStarted");
+
+    this._cancelDelayedStartup();
+
+    // Bug 1531854 - The hidden window is force-created here
+    // until all of its dependencies are handled.
+    Services.appShell.hiddenDOMWindow;
+
+    gBrowser.addEventListener(
+      "PermissionStateChange",
+      function () {
+        gIdentityHandler.refreshIdentityBlock();
+        gPermissionPanel.updateSharingIndicator();
+      },
+      true
+    );
+
+    this._handleURIToLoad();
+
+    Services.obs.addObserver(gIdentityHandler, "perm-changed");
+    Services.obs.addObserver(gRemoteControl, "devtools-socket");
+    Services.obs.addObserver(gRemoteControl, "marionette-listening");
+    Services.obs.addObserver(gRemoteControl, "remote-listening");
+    Services.obs.addObserver(
+      gSessionHistoryObserver,
+      "browser:purge-session-history"
+    );
+    Services.obs.addObserver(
+      gStoragePressureObserver,
+      "QuotaManager::StoragePressure"
+    );
+    Services.obs.addObserver(gXPInstallObserver, "addon-install-disabled");
+    Services.obs.addObserver(gXPInstallObserver, "addon-install-started");
+    Services.obs.addObserver(gXPInstallObserver, "addon-install-blocked");
+    Services.obs.addObserver(
+      gXPInstallObserver,
+      "addon-install-fullscreen-blocked"
+    );
+    Services.obs.addObserver(
+      gXPInstallObserver,
+      "addon-install-origin-blocked"
+    );
+    Services.obs.addObserver(
+      gXPInstallObserver,
+      "addon-install-policy-blocked"
+    );
+    Services.obs.addObserver(
+      gXPInstallObserver,
+      "addon-install-webapi-blocked"
+    );
+    Services.obs.addObserver(gXPInstallObserver, "addon-install-failed");
+    Services.obs.addObserver(gXPInstallObserver, "addon-install-confirmation");
+    Services.obs.addObserver(gKeywordURIFixup, "keyword-uri-fixup");
+
+    BrowserOffline.init();
+    CanvasPermissionPromptHelper.init();
+    WebAuthnPromptHelper.init();
+    ContentAnalysis.initialize(document);
+
+    // Initialize the full zoom setting.
+    // We do this before the session restore service gets initialized so we can
+    // apply full zoom settings to tabs restored by the session restore service.
+    FullZoom.init();
+    PanelUI.init(shouldSuppressPopupNotifications);
+    ReportBrokenSite.init(gBrowser);
+
+    UpdateUrlbarSearchSplitterState();
+
+    BookmarkingUI.init();
+    BrowserSearch.delayedStartupInit();
+    SearchUIUtils.init();
+    gProtectionsHandler.init();
+    HomePage.delayedStartup().catch(console.error);
+
+    let safeMode = document.getElementById("helpSafeMode");
+    if (Services.appinfo.inSafeMode) {
+      document.l10n.setAttributes(safeMode, "menu-help-exit-troubleshoot-mode");
+      safeMode.setAttribute(
+        "appmenu-data-l10n-id",
+        "appmenu-help-exit-troubleshoot-mode"
+      );
+    }
+
+    // BiDi UI
+    gBidiUI = isBidiEnabled();
+    if (gBidiUI) {
+      document.getElementById("documentDirection-separator").hidden = false;
+      document.getElementById("documentDirection-swap").hidden = false;
+      document.getElementById("textfieldDirection-separator").hidden = false;
+      document.getElementById("textfieldDirection-swap").hidden = false;
+    }
+
+    // Setup click-and-hold gestures access to the session history
+    // menus if global click-and-hold isn't turned on
+    if (!Services.prefs.getBoolPref("ui.click_hold_context_menus", false)) {
+      SetClickAndHoldHandlers();
+    }
+
+    function initBackForwardButtonTooltip(tooltipId, l10nId, shortcutId) {
+      let shortcut = document.getElementById(shortcutId);
+      shortcut = ShortcutUtils.prettifyShortcut(shortcut);
+
+      let tooltip = document.getElementById(tooltipId);
+      document.l10n.setAttributes(tooltip, l10nId, { shortcut });
+    }
+
+    initBackForwardButtonTooltip(
+      "back-button-tooltip-description",
+      "navbar-tooltip-back-2",
+      "goBackKb"
+    );
+
+    initBackForwardButtonTooltip(
+      "forward-button-tooltip-description",
+      "navbar-tooltip-forward-2",
+      "goForwardKb"
+    );
+
+    PlacesToolbarHelper.init();
+
+    ctrlTab.readPref();
+    Services.prefs.addObserver(ctrlTab.prefName, ctrlTab);
+
+    // The object handling the downloads indicator is initialized here in the
+    // delayed startup function, but the actual indicator element is not loaded
+    // unless there are downloads to be displayed.
+    DownloadsButton.initializeIndicator();
+
+    if (AppConstants.platform != "macosx") {
+      updateEditUIVisibility();
+      let placesContext = document.getElementById("placesContext");
+      placesContext.addEventListener("popupshowing", updateEditUIVisibility);
+      placesContext.addEventListener("popuphiding", updateEditUIVisibility);
+    }
+
+    FullScreen.init();
+    MenuTouchModeObserver.init();
+
+    if (AppConstants.MOZ_DATA_REPORTING) {
+      gDataNotificationInfoBar.init();
+    }
+
+    if (!AppConstants.MOZILLA_OFFICIAL) {
+      DevelopmentHelpers.init();
+    }
+
+    gExtensionsNotifications.init();
+
+    let wasMinimized = window.windowState == window.STATE_MINIMIZED;
+    window.addEventListener("sizemodechange", () => {
+      let isMinimized = window.windowState == window.STATE_MINIMIZED;
+      if (wasMinimized != isMinimized) {
+        wasMinimized = isMinimized;
+        UpdatePopupNotificationsVisibility();
+      }
+    });
+
+    window.addEventListener("mousemove", MousePosTracker);
+    window.addEventListener("dragover", MousePosTracker);
+
+    gNavToolbox.addEventListener("customizationstarting", CustomizationHandler);
+    gNavToolbox.addEventListener("aftercustomization", CustomizationHandler);
+
+    SessionStore.promiseInitialized.then(() => {
+      // Bail out if the window has been closed in the meantime.
+      if (window.closed) {
+        return;
+      }
+
+      // Enable the Restore Last Session command if needed
+      RestoreLastSessionObserver.init();
+
+      SidebarController.startDelayedLoad();
+
+      PanicButtonNotifier.init();
+    });
+
+    if (BrowserHandler.kiosk) {
+      // We don't modify popup windows for kiosk mode
+      if (!gURLBar.readOnly) {
+        window.fullScreen = true;
+      }
+    }
+
+    if (Services.policies.status === Services.policies.ACTIVE) {
+      if (!Services.policies.isAllowed("hideShowMenuBar")) {
+        document
+          .getElementById("toolbar-menubar")
+          .removeAttribute("toolbarname");
+      }
+      if (!Services.policies.isAllowed("filepickers")) {
+        let savePageCommand = document.getElementById("Browser:SavePage");
+        let openFileCommand = document.getElementById("Browser:OpenFile");
+
+        savePageCommand.setAttribute("disabled", "true");
+        openFileCommand.setAttribute("disabled", "true");
+
+        document.addEventListener("FilePickerBlocked", function (event) {
+          let browser = event.target;
+
+          let notificationBox = browser
+            .getTabBrowser()
+            ?.getNotificationBox(browser);
+
+          // Prevent duplicate notifications
+          if (
+            notificationBox &&
+            !notificationBox.getNotificationWithValue("filepicker-blocked")
+          ) {
+            notificationBox.appendNotification("filepicker-blocked", {
+              label: {
+                "l10n-id": "filepicker-blocked-infobar",
+              },
+              priority: notificationBox.PRIORITY_INFO_LOW,
+            });
+          }
+        });
+      }
+      let policies = Services.policies.getActivePolicies();
+      if ("ManagedBookmarks" in policies) {
+        let managedBookmarks = policies.ManagedBookmarks;
+        let children = managedBookmarks.filter(
+          child => !("toplevel_name" in child)
+        );
+        if (children.length) {
+          let managedBookmarksButton =
+            document.createXULElement("toolbarbutton");
+          managedBookmarksButton.setAttribute("id", "managed-bookmarks");
+          managedBookmarksButton.setAttribute("class", "bookmark-item");
+          let toplevel = managedBookmarks.find(
+            element => "toplevel_name" in element
+          );
+          if (toplevel) {
+            managedBookmarksButton.setAttribute(
+              "label",
+              toplevel.toplevel_name
+            );
+          } else {
+            document.l10n.setAttributes(
+              managedBookmarksButton,
+              "managed-bookmarks"
+            );
+          }
+          managedBookmarksButton.setAttribute("context", "placesContext");
+          managedBookmarksButton.setAttribute("container", "true");
+          managedBookmarksButton.setAttribute("removable", "false");
+          managedBookmarksButton.setAttribute("type", "menu");
+
+          let managedBookmarksPopup = document.createXULElement("menupopup");
+          managedBookmarksPopup.setAttribute("id", "managed-bookmarks-popup");
+          managedBookmarksPopup.setAttribute(
+            "oncommand",
+            "PlacesToolbarHelper.openManagedBookmark(event);"
+          );
+          managedBookmarksPopup.setAttribute(
+            "ondragover",
+            "event.dataTransfer.effectAllowed='none';"
+          );
+          managedBookmarksPopup.setAttribute(
+            "ondragstart",
+            "PlacesToolbarHelper.onDragStartManaged(event);"
+          );
+          managedBookmarksPopup.setAttribute(
+            "onpopupshowing",
+            "PlacesToolbarHelper.populateManagedBookmarks(this);"
+          );
+          managedBookmarksPopup.setAttribute("placespopup", "true");
+          managedBookmarksPopup.setAttribute("is", "places-popup");
+          managedBookmarksPopup.classList.add("toolbar-menupopup");
+          managedBookmarksButton.appendChild(managedBookmarksPopup);
+
+          gNavToolbox.palette.appendChild(managedBookmarksButton);
+
+          CustomizableUI.ensureWidgetPlacedInWindow(
+            "managed-bookmarks",
+            window
+          );
+
+          // Add button if it doesn't exist
+          if (!CustomizableUI.getPlacementOfWidget("managed-bookmarks")) {
+            CustomizableUI.addWidgetToArea(
+              "managed-bookmarks",
+              CustomizableUI.AREA_BOOKMARKS,
+              0
+            );
+          }
+        }
+      }
+    }
+
+    CaptivePortalWatcher.delayedStartup();
+
+    ShoppingSidebarManager.ensureInitialized();
+
+    SessionStore.promiseAllWindowsRestored.then(() => {
+      this._schedulePerWindowIdleTasks();
+      document.documentElement.setAttribute("sessionrestored", "true");
+    });
+
+    this.delayedStartupFinished = true;
+    _resolveDelayedStartup();
+    Services.obs.notifyObservers(window, "browser-delayed-startup-finished");
+    TelemetryTimestamps.add("delayedStartupFinished");
+    // We've announced that delayed startup has finished. Do not add code past this point.
+  },
+
+  /**
+   * Resolved on the first MozLayerTreeReady and next MozAfterPaint in the
+   * parent process.
+   */
+  get firstContentWindowPaintPromise() {
+    return this._firstContentWindowPaintDeferred.promise;
+  },
+
+  _setInitialFocus() {
+    let initiallyFocusedElement = document.commandDispatcher.focusedElement;
+
+    // To prevent startup flicker, the urlbar has the 'focused' attribute set
+    // by default. If we are not sure the urlbar will be focused in this
+    // window, we need to remove the attribute before first paint.
+    // TODO (bug 1629956): The urlbar having the 'focused' attribute by default
+    // isn't a useful optimization anymore since UrlbarInput needs layout
+    // information to focus the urlbar properly.
+    let shouldRemoveFocusedAttribute = true;
+
+    this._callWithURIToLoad(uriToLoad => {
+      if (
+        isBlankPageURL(uriToLoad) ||
+        uriToLoad == "about:privatebrowsing" ||
+        this.getTabToAdopt()?.isEmpty
+      ) {
+        gURLBar.select();
+        shouldRemoveFocusedAttribute = false;
+        return;
+      }
+
+      // If the initial browser is remote, in order to optimize for first paint,
+      // we'll defer switching focus to that browser until it has painted.
+      // Otherwise use a regular promise to guarantee that mutationobserver
+      // microtasks that could affect focusability have run.
+      let promise = gBrowser.selectedBrowser.isRemoteBrowser
+        ? this.firstContentWindowPaintPromise
+        : Promise.resolve();
+
+      promise.then(() => {
+        // If focus didn't move while we were waiting, we're okay to move to
+        // the browser.
+        if (
+          document.commandDispatcher.focusedElement == initiallyFocusedElement
+        ) {
+          gBrowser.selectedBrowser.focus();
+        }
+      });
+    });
+
+    // Delay removing the attribute using requestAnimationFrame to avoid
+    // invalidating styles multiple times in a row if uriToLoadPromise
+    // resolves before first paint.
+    if (shouldRemoveFocusedAttribute) {
+      window.requestAnimationFrame(() => {
+        if (shouldRemoveFocusedAttribute) {
+          gURLBar.removeAttribute("focused");
+        }
+      });
+    }
+  },
+
+  _handleURIToLoad() {
+    this._callWithURIToLoad(uriToLoad => {
+      if (!uriToLoad) {
+        // We don't check whether window.arguments[5] (userContextId) is set
+        // because tabbrowser.js takes care of that for the initial tab.
+        return;
+      }
+
+      // We don't check if uriToLoad is a XULElement because this case has
+      // already been handled before first paint, and the argument cleared.
+      if (Array.isArray(uriToLoad)) {
+        // This function throws for certain malformed URIs, so use exception handling
+        // so that we don't disrupt startup
+        try {
+          gBrowser.loadTabs(uriToLoad, {
+            inBackground: false,
+            replace: true,
+            // See below for the semantics of window.arguments. Only the minimum is supported.
+            userContextId: window.arguments[5],
+            triggeringPrincipal:
+              window.arguments[8] ||
+              Services.scriptSecurityManager.getSystemPrincipal(),
+            allowInheritPrincipal: window.arguments[9],
+            csp: window.arguments[10],
+            fromExternal: true,
+          });
+        } catch (e) {}
+      } else if (window.arguments.length >= 3) {
+        // window.arguments[1]: extraOptions (nsIPropertyBag)
+        //                 [2]: referrerInfo (nsIReferrerInfo)
+        //                 [3]: postData (nsIInputStream)
+        //                 [4]: allowThirdPartyFixup (bool)
+        //                 [5]: userContextId (int)
+        //                 [6]: originPrincipal (nsIPrincipal)
+        //                 [7]: originStoragePrincipal (nsIPrincipal)
+        //                 [8]: triggeringPrincipal (nsIPrincipal)
+        //                 [9]: allowInheritPrincipal (bool)
+        //                 [10]: csp (nsIContentSecurityPolicy)
+        //                 [11]: nsOpenWindowInfo
+        let userContextId =
+          window.arguments[5] != undefined
+            ? window.arguments[5]
+            : Ci.nsIScriptSecurityManager.DEFAULT_USER_CONTEXT_ID;
+
+        let hasValidUserGestureActivation = undefined;
+        let fromExternal = undefined;
+        let globalHistoryOptions = undefined;
+        let triggeringRemoteType = undefined;
+        let forceAllowDataURI = false;
+        let wasSchemelessInput = false;
+        if (window.arguments[1]) {
+          if (!(window.arguments[1] instanceof Ci.nsIPropertyBag2)) {
+            throw new Error(
+              "window.arguments[1] must be null or Ci.nsIPropertyBag2!"
+            );
+          }
+
+          let extraOptions = window.arguments[1];
+          if (extraOptions.hasKey("hasValidUserGestureActivation")) {
+            hasValidUserGestureActivation = extraOptions.getPropertyAsBool(
+              "hasValidUserGestureActivation"
+            );
+          }
+          if (extraOptions.hasKey("fromExternal")) {
+            fromExternal = extraOptions.getPropertyAsBool("fromExternal");
+          }
+          if (extraOptions.hasKey("triggeringSponsoredURL")) {
+            globalHistoryOptions = {
+              triggeringSponsoredURL: extraOptions.getPropertyAsACString(
+                "triggeringSponsoredURL"
+              ),
+            };
+            if (extraOptions.hasKey("triggeringSponsoredURLVisitTimeMS")) {
+              globalHistoryOptions.triggeringSponsoredURLVisitTimeMS =
+                extraOptions.getPropertyAsUint64(
+                  "triggeringSponsoredURLVisitTimeMS"
+                );
+            }
+          }
+          if (extraOptions.hasKey("triggeringRemoteType")) {
+            triggeringRemoteType = extraOptions.getPropertyAsACString(
+              "triggeringRemoteType"
+            );
+          }
+          if (extraOptions.hasKey("forceAllowDataURI")) {
+            forceAllowDataURI =
+              extraOptions.getPropertyAsBool("forceAllowDataURI");
+          }
+          if (extraOptions.hasKey("wasSchemelessInput")) {
+            wasSchemelessInput =
+              extraOptions.getPropertyAsBool("wasSchemelessInput");
+          }
+        }
+
+        try {
+          openLinkIn(uriToLoad, "current", {
+            referrerInfo: window.arguments[2] || null,
+            postData: window.arguments[3] || null,
+            allowThirdPartyFixup: window.arguments[4] || false,
+            userContextId,
+            // pass the origin principal (if any) and force its use to create
+            // an initial about:blank viewer if present:
+            originPrincipal: window.arguments[6],
+            originStoragePrincipal: window.arguments[7],
+            triggeringPrincipal: window.arguments[8],
+            // TODO fix allowInheritPrincipal to default to false.
+            // Default to true unless explicitly set to false because of bug 1475201.
+            allowInheritPrincipal: window.arguments[9] !== false,
+            csp: window.arguments[10],
+            forceAboutBlankViewerInCurrent: !!window.arguments[6],
+            forceAllowDataURI,
+            hasValidUserGestureActivation,
+            fromExternal,
+            globalHistoryOptions,
+            triggeringRemoteType,
+            wasSchemelessInput,
+          });
+        } catch (e) {
+          console.error(e);
+        }
+
+        window.focus();
+      } else {
+        // Note: loadOneOrMoreURIs *must not* be called if window.arguments.length >= 3.
+        // Such callers expect that window.arguments[0] is handled as a single URI.
+        loadOneOrMoreURIs(
+          uriToLoad,
+          Services.scriptSecurityManager.getSystemPrincipal(),
+          null
+        );
+      }
+    });
+  },
+
+  /**
+   * Use this function as an entry point to schedule tasks that
+   * need to run once per window after startup, and can be scheduled
+   * by using an idle callback.
+   *
+   * The functions scheduled here will fire from idle callbacks
+   * once every window has finished being restored by session
+   * restore, and after the equivalent only-once tasks
+   * have run (from _scheduleStartupIdleTasks in BrowserGlue.sys.mjs).
+   */
+  _schedulePerWindowIdleTasks() {
+    // Bail out if the window has been closed in the meantime.
+    if (window.closed) {
+      return;
+    }
+
+    function scheduleIdleTask(func, options) {
+      requestIdleCallback(function idleTaskRunner() {
+        if (!window.closed) {
+          func();
+        }
+      }, options);
+    }
+
+    scheduleIdleTask(() => {
+      // Initialize the Sync UI
+      gSync.init();
+    });
+
+    scheduleIdleTask(() => {
+      // Read prefers-reduced-motion setting
+      let reduceMotionQuery = window.matchMedia(
+        "(prefers-reduced-motion: reduce)"
+      );
+      function readSetting() {
+        gReduceMotionSetting = reduceMotionQuery.matches;
+      }
+      reduceMotionQuery.addListener(readSetting);
+      readSetting();
+    });
+
+    scheduleIdleTask(() => {
+      // setup simple gestures support
+      gGestureSupport.init(true);
+
+      // setup history swipe animation
+      gHistorySwipeAnimation.init();
+    });
+
+    scheduleIdleTask(() => {
+      gBrowserThumbnails.init();
+    });
+
+    scheduleIdleTask(
+      () => {
+        // Initialize the download manager some time after the app starts so that
+        // auto-resume downloads begin (such as after crashing or quitting with
+        // active downloads) and speeds up the first-load of the download manager UI.
+        // If the user manually opens the download manager before the timeout, the
+        // downloads will start right away, and initializing again won't hurt.
+        try {
+          DownloadsCommon.initializeAllDataLinks();
+          ChromeUtils.importESModule(
+            "resource:///modules/DownloadsTaskbar.sys.mjs"
+          ).DownloadsTaskbar.registerIndicator(window);
+          if (AppConstants.platform == "macosx") {
+            ChromeUtils.importESModule(
+              "resource:///modules/DownloadsMacFinderProgress.sys.mjs"
+            ).DownloadsMacFinderProgress.register();
+          }
+          Services.telemetry.setEventRecordingEnabled("downloads", true);
+        } catch (ex) {
+          console.error(ex);
+        }
+      },
+      { timeout: 10000 }
+    );
+
+    if (Win7Features) {
+      scheduleIdleTask(() => Win7Features.onOpenWindow());
+    }
+
+    scheduleIdleTask(async () => {
+      NewTabPagePreloading.maybeCreatePreloadedBrowser(window);
+    });
+
+    scheduleIdleTask(() => {
+      gGfxUtils.init();
+    });
+
+    // This should always go last, since the idle tasks (except for the ones with
+    // timeouts) should execute in order. Note that this observer notification is
+    // not guaranteed to fire, since the window could close before we get here.
+    scheduleIdleTask(() => {
+      this.idleTasksFinished.resolve();
+      Services.obs.notifyObservers(
+        window,
+        "browser-idle-startup-tasks-finished"
+      );
+    });
+
+    scheduleIdleTask(() => {
+      gProfiles.init();
+    });
+  },
+
+  // Returns the URI(s) to load at startup if it is immediately known, or a
+  // promise resolving to the URI to load.
+  get uriToLoadPromise() {
+    delete this.uriToLoadPromise;
+    return (this.uriToLoadPromise = (function () {
+      // window.arguments[0]: URI to load (string), or an nsIArray of
+      //                      nsISupportsStrings to load, or a xul:tab of
+      //                      a tabbrowser, which will be replaced by this
+      //                      window (for this case, all other arguments are
+      //                      ignored).
+      let uri = window.arguments?.[0];
+      if (!uri || window.XULElement.isInstance(uri)) {
+        return null;
+      }
+
+      let defaultArgs = BrowserHandler.defaultArgs;
+
+      // If the given URI is different from the homepage, we want to load it.
+      if (uri != defaultArgs) {
+        AboutNewTab.noteNonDefaultStartup();
+
+        if (uri instanceof Ci.nsIArray) {
+          // Transform the nsIArray of nsISupportsString's into a JS Array of
+          // JS strings.
+          return Array.from(
+            uri.enumerate(Ci.nsISupportsString),
+            supportStr => supportStr.data
+          );
+        } else if (uri instanceof Ci.nsISupportsString) {
+          return uri.data;
+        }
+        return uri;
+      }
+
+      // The URI appears to be the the homepage. We want to load it only if
+      // session restore isn't about to override the homepage.
+      let willOverride = SessionStartup.willOverrideHomepage;
+      if (typeof willOverride == "boolean") {
+        return willOverride ? null : uri;
+      }
+      return willOverride.then(willOverrideHomepage =>
+        willOverrideHomepage ? null : uri
+      );
+    })());
+  },
+
+  // Calls the given callback with the URI to load at startup.
+  // Synchronously if possible, or after uriToLoadPromise resolves otherwise.
+  _callWithURIToLoad(callback) {
+    let uriToLoad = this.uriToLoadPromise;
+    if (uriToLoad && uriToLoad.then) {
+      uriToLoad.then(callback);
+    } else {
+      callback(uriToLoad);
+    }
+  },
+
+  onUnload() {
+    gUIDensity.uninit();
+
+    TabsInTitlebar.uninit();
+
+    ToolbarIconColor.uninit();
+
+    // In certain scenarios it's possible for unload to be fired before onload,
+    // (e.g. if the window is being closed after browser.js loads but before the
+    // load completes). In that case, there's nothing to do here.
+    if (!this._loadHandled) {
+      return;
+    }
+
+    // First clean up services initialized in gBrowserInit.onLoad (or those whose
+    // uninit methods don't depend on the services having been initialized).
+
+    CombinedStopReload.uninit();
+
+    gGestureSupport.init(false);
+
+    gHistorySwipeAnimation.uninit();
+
+    FullScreen.uninit();
+
+    gSync.uninit();
+
+    gExtensionsNotifications.uninit();
+    gUnifiedExtensions.uninit();
+
+    try {
+      gBrowser.removeProgressListener(window.XULBrowserWindow);
+      gBrowser.removeTabsProgressListener(window.TabsProgressListener);
+    } catch (ex) {}
+
+    PlacesToolbarHelper.uninit();
+
+    BookmarkingUI.uninit();
+
+    TabletModeUpdater.uninit();
+
+    gTabletModePageCounter.finish();
+
+    CaptivePortalWatcher.uninit();
+
+    SidebarController.uninit();
+
+    DownloadsButton.uninit();
+
+    if (gToolbarKeyNavEnabled) {
+      ToolbarKeyboardNavigator.uninit();
+    }
+
+    BrowserSearch.uninit();
+
+    NewTabPagePreloading.removePreloadedBrowser(window);
+
+    FirefoxViewHandler.uninit();
+
+    // Now either cancel delayedStartup, or clean up the services initialized from
+    // it.
+    if (this._boundDelayedStartup) {
+      this._cancelDelayedStartup();
+    } else {
+      if (Win7Features) {
+        Win7Features.onCloseWindow();
+      }
+      Services.prefs.removeObserver(ctrlTab.prefName, ctrlTab);
+      ctrlTab.uninit();
+      gBrowserThumbnails.uninit();
+      gProtectionsHandler.uninit();
+      FullZoom.destroy();
+
+      Services.obs.removeObserver(gIdentityHandler, "perm-changed");
+      Services.obs.removeObserver(gRemoteControl, "devtools-socket");
+      Services.obs.removeObserver(gRemoteControl, "marionette-listening");
+      Services.obs.removeObserver(gRemoteControl, "remote-listening");
+      Services.obs.removeObserver(
+        gSessionHistoryObserver,
+        "browser:purge-session-history"
+      );
+      Services.obs.removeObserver(
+        gStoragePressureObserver,
+        "QuotaManager::StoragePressure"
+      );
+      Services.obs.removeObserver(gXPInstallObserver, "addon-install-disabled");
+      Services.obs.removeObserver(gXPInstallObserver, "addon-install-started");
+      Services.obs.removeObserver(gXPInstallObserver, "addon-install-blocked");
+      Services.obs.removeObserver(
+        gXPInstallObserver,
+        "addon-install-fullscreen-blocked"
+      );
+      Services.obs.removeObserver(
+        gXPInstallObserver,
+        "addon-install-origin-blocked"
+      );
+      Services.obs.removeObserver(
+        gXPInstallObserver,
+        "addon-install-policy-blocked"
+      );
+      Services.obs.removeObserver(
+        gXPInstallObserver,
+        "addon-install-webapi-blocked"
+      );
+      Services.obs.removeObserver(gXPInstallObserver, "addon-install-failed");
+      Services.obs.removeObserver(
+        gXPInstallObserver,
+        "addon-install-confirmation"
+      );
+      Services.obs.removeObserver(gKeywordURIFixup, "keyword-uri-fixup");
+
+      MenuTouchModeObserver.uninit();
+      BrowserOffline.uninit();
+      CanvasPermissionPromptHelper.uninit();
+      WebAuthnPromptHelper.uninit();
+      PanelUI.uninit();
+    }
+
+    // Final window teardown, do this last.
+    gBrowser.destroy();
+    window.XULBrowserWindow = null;
+    window.docShell.treeOwner
+      .QueryInterface(Ci.nsIInterfaceRequestor)
+      .getInterface(Ci.nsIAppWindow).XULBrowserWindow = null;
+    window.browserDOMWindow = null;
+  },
+};
+
+gBrowserInit.idleTasksFinishedPromise = gBrowserInit.idleTasksFinished.promise;
diff --git a/browser/base/content/browser-menubar.inc b/browser/base/content/browser-menubar.inc
index 0c8b4a1cf6..0eebfea75a 100644
--- a/browser/base/content/browser-menubar.inc
+++ b/browser/base/content/browser-menubar.inc
@@ -140,22 +140,7 @@
                   </menupopup>
                 </menu>
                 <menu id="viewSidebarMenuMenu" data-l10n-id="menu-view-sidebar">
-                  <menupopup id="viewSidebarMenu" onpopupshowing="SidebarUI.setMegalistMenubarVisibility(event);">
-                    <menuitem id="menu_bookmarksSidebar"
-                              type="checkbox"
-                              key="viewBookmarksSidebarKb"
-                              oncommand="SidebarUI.toggle('viewBookmarksSidebar');" data-l10n-id="menu-view-bookmarks"/>
-                    <menuitem id="menu_historySidebar"
-                              type="checkbox"
-                              key="key_gotoHistory"
-                              oncommand="SidebarUI.toggle('viewHistorySidebar');" data-l10n-id="menu-view-history-button"/>
-                    <menuitem id="menu_tabsSidebar"
-                              type="checkbox"
-                              class="sync-ui-item"
-                              oncommand="SidebarUI.toggle('viewTabsSidebar');" data-l10n-id="menu-view-synced-tabs-sidebar"/>
-                    <menuitem id="menu_megalistSidebar"
-                              type="checkbox"
-                              oncommand="SidebarUI.toggle('viewMegalistSidebar');" data-l10n-id="menu-view-megalist-sidebar"/>
+                  <menupopup id="viewSidebarMenu" onpopupshowing="SidebarController.setMegalistMenubarVisibility(event);">
                   </menupopup>
                 </menu>
                 <menuseparator/>
@@ -192,7 +177,7 @@
                 </menu>
                 <menuitem id="repair-text-encoding"
                           disabled="true"
-                          oncommand="BrowserForceEncodingDetection();"
+                          oncommand="BrowserCommands.forceEncodingDetection();"
                           data-l10n-id="menu-view-repair-text-encoding"/>
                 <menuseparator/>
 #ifdef XP_MACOSX
diff --git a/browser/base/content/browser-pageActions.js b/browser/base/content/browser-pageActions.js
index 1fd1062948..fe0453160d 100644
--- a/browser/base/content/browser-pageActions.js
+++ b/browser/base/content/browser-pageActions.js
@@ -970,7 +970,7 @@ var BrowserPageActions = {
     this._contextAction = null;
 
     let viewID = "addons://detail/" + encodeURIComponent(action.extensionID);
-    window.BrowserOpenAddonsMgr(viewID);
+    window.BrowserAddonUI.openAddonsMgr(viewID);
   },
 
   /**
diff --git a/browser/base/content/browser-places.js b/browser/base/content/browser-places.js
index c940fade5f..404a080983 100644
--- a/browser/base/content/browser-places.js
+++ b/browser/base/content/browser-places.js
@@ -55,7 +55,6 @@ var StarUI = {
     delete this.panel;
     this._createPanelIfNeeded();
     var element = this._element("editBookmarkPanel");
-    window.ensureCustomElements("moz-button-group");
     // initially the panel is hidden
     // to avoid impacting startup / new window performance
     element.hidden = false;
@@ -1378,7 +1377,7 @@ var BookmarkingUI = {
 
     this.updateLabel(
       "BMB_viewBookmarksSidebar",
-      SidebarUI.currentID == "viewBookmarksSidebar"
+      SidebarController.currentID == "viewBookmarksSidebar"
     );
     this.updateLabel("BMB_viewBookmarksToolbar", !this.toolbar.collapsed);
   },
@@ -1999,6 +1998,13 @@ var BookmarkingUI = {
       case "ViewHiding":
         this.onPanelMenuViewHiding(aEvent);
         break;
+      case "command":
+        if (aEvent.target.id == "panelMenu_searchBookmarks") {
+          PlacesCommandHook.searchBookmarks();
+        } else if (aEvent.target.id == "panelMenu_viewBookmarksToolbar") {
+          this.toggleBookmarksToolbar("bookmark-tools");
+        }
+        break;
     }
   },
 
@@ -2026,12 +2032,15 @@ var BookmarkingUI = {
       panelview
     );
     panelview.removeEventListener("ViewShowing", this);
+    panelview.addEventListener("command", this);
   },
 
   onPanelMenuViewHiding: function BUI_onViewHiding(aEvent) {
     this._panelMenuView.uninit();
     delete this._panelMenuView;
-    aEvent.target.removeEventListener("ViewHiding", this);
+    let panelview = aEvent.target;
+    panelview.removeEventListener("ViewHiding", this);
+    panelview.removeEventListener("command", this);
   },
 
   handlePlacesEvents(aEvents) {
diff --git a/browser/base/content/browser-sets.inc b/browser/base/content/browser-sets.inc
index e247f0641e..f77ce1661e 100644
--- a/browser/base/content/browser-sets.inc
+++ b/browser/base/content/browser-sets.inc
@@ -91,8 +91,8 @@
     <command id="Browser:NewUserContextTab" oncommand="openNewUserContextTab(event.sourceEvent);"/>
     <command id="Browser:OpenAboutContainers" oncommand="openPreferences('paneContainers');"/>
     <command id="Tools:Search" oncommand="BrowserSearch.webSearch();"/>
-    <command id="Tools:Downloads" oncommand="BrowserDownloadsUI();"/>
-    <command id="Tools:Addons" oncommand="BrowserOpenAddonsMgr();"/>
+    <command id="Tools:Downloads" oncommand="BrowserCommands.downloadsUI();"/>
+    <command id="Tools:Addons" oncommand="BrowserAddonUI.openAddonsMgr();"/>
     <command id="Tools:Sanitize" oncommand="Sanitizer.showUI(window);"/>
     <command id="Tools:PrivateBrowsing"
       oncommand="OpenBrowserWindow({private: true});"/>
@@ -276,7 +276,7 @@
     <key id="viewBookmarksSidebarKb"
          data-l10n-id="bookmark-show-sidebar-shortcut"
          modifiers="accel"
-         oncommand="SidebarUI.toggle('viewBookmarksSidebar');"/>
+         oncommand="SidebarController.toggle('viewBookmarksSidebar');"/>
     <key id="viewBookmarksToolbarKb"
          data-l10n-id="bookmark-show-toolbar-shortcut"
          oncommand="BookmarkingUI.toggleBookmarksToolbar('shortcut');"
@@ -295,7 +295,7 @@
 #else
          modifiers="accel"
 #endif
-         oncommand="SidebarUI.toggle('viewHistorySidebar');"/>
+         oncommand="SidebarController.toggle('viewHistorySidebar');"/>
 
     <key id="key_fullZoomReduce" data-l10n-id="full-zoom-reduce-shortcut" command="cmd_fullZoomReduce"  modifiers="accel"/>
     <key                         data-l10n-id="full-zoom-reduce-shortcut-alt-a" command="cmd_fullZoomReduce"  modifiers="accel"/>
diff --git a/browser/base/content/browser-siteIdentity.js b/browser/base/content/browser-siteIdentity.js
index 60bd4fc01c..eaed3950fe 100644
--- a/browser/base/content/browser-siteIdentity.js
+++ b/browser/base/content/browser-siteIdentity.js
@@ -177,7 +177,6 @@ var gIdentityHandler = {
 
   _popupInitialized: false,
   _initializePopup() {
-    window.ensureCustomElements("moz-support-link");
     if (!this._popupInitialized) {
       let wrapper = document.getElementById("template-identity-popup");
       wrapper.replaceWith(wrapper.content);
diff --git a/browser/base/content/browser-sitePermissionPanel.js b/browser/base/content/browser-sitePermissionPanel.js
index d977653f51..de7b2cc39a 100644
--- a/browser/base/content/browser-sitePermissionPanel.js
+++ b/browser/base/content/browser-sitePermissionPanel.js
@@ -14,9 +14,6 @@ var gPermissionPanel = {
     if (!this._popupInitialized) {
       let wrapper = document.getElementById("template-permission-popup");
       wrapper.replaceWith(wrapper.content);
-
-      window.ensureCustomElements("moz-support-link");
-
       this._popupInitialized = true;
     }
   },
diff --git a/browser/base/content/browser-siteProtections.js b/browser/base/content/browser-siteProtections.js
index 043dc53b95..31b87ac7e0 100644
--- a/browser/base/content/browser-siteProtections.js
+++ b/browser/base/content/browser-siteProtections.js
@@ -1377,7 +1377,6 @@ var gProtectionsHandler = {
       let wrapper = document.getElementById("template-protections-popup");
       this._protectionsPopup = wrapper.content.firstElementChild;
       wrapper.replaceWith(wrapper.content);
-      window.ensureCustomElements("moz-support-link");
 
       this.maybeSetMilestoneCounterText();
 
@@ -1591,8 +1590,6 @@ var gProtectionsHandler = {
 
     // Add an observer to observe that the history has been cleared.
     Services.obs.addObserver(this, "browser:purge-session-history");
-
-    window.ensureCustomElements("moz-button-group", "moz-toggle");
   },
 
   uninit() {
@@ -2601,14 +2598,14 @@ var gProtectionsHandler = {
   _createHeroElement(doc, message) {
     const messageEl = this._createElement(doc, "div");
     messageEl.setAttribute("id", "protections-popup-message");
-    messageEl.classList.add("whatsNew-hero-message");
+    messageEl.classList.add("protections-hero-message");
     const wrapperEl = this._createElement(doc, "div");
-    wrapperEl.classList.add("whatsNew-message-body");
+    wrapperEl.classList.add("protections-popup-message-body");
     messageEl.appendChild(wrapperEl);
 
     wrapperEl.appendChild(
       this._createElement(doc, "h2", {
-        classList: "whatsNew-message-title",
+        classList: "protections-popup-message-title",
         content: message.content.title,
       })
     );
diff --git a/browser/base/content/browser-sync.js b/browser/base/content/browser-sync.js
index 065546d7b8..9aa6cc5cd4 100644
--- a/browser/base/content/browser-sync.js
+++ b/browser/base/content/browser-sync.js
@@ -202,10 +202,7 @@ this.SyncedTabsPanelList = class SyncedTabsPanelList {
   }
 
   _appendSyncClient(client, container, labelId, paginationInfo) {
-    let {
-      maxTabs = SyncedTabsPanelList.sRemoteTabsPerPage,
-      showInactive = false,
-    } = paginationInfo;
+    let { maxTabs = SyncedTabsPanelList.sRemoteTabsPerPage } = paginationInfo;
     // Create the element for the remote client.
     let clientItem = document.createXULElement("label");
     clientItem.setAttribute("id", labelId);
@@ -227,11 +224,24 @@ this.SyncedTabsPanelList = class SyncedTabsPanelList {
       );
       label.setAttribute("class", "PanelUI-remotetabs-notabsforclient-label");
     } else {
-      let tabs = client.tabs.filter(t => showInactive || !t.inactive);
-      let numInactive = client.tabs.length - tabs.length;
+      // We have the client obj but we need the FxA device obj so we use the clients
+      // engine to get us the FxA device
+      let device =
+        fxAccounts.device.recentDeviceList &&
+        fxAccounts.device.recentDeviceList.find(
+          d =>
+            d.id === Weave.Service.clientsEngine.getClientFxaDeviceId(client.id)
+        );
+      let remoteTabCloseAvailable =
+        device && fxAccounts.commands.closeTab.isDeviceCompatible(device);
+
+      let tabs = client.tabs.filter(t => !t.inactive);
+      let hasInactive = tabs.length != client.tabs.length;
 
-      // If this page will display all tabs, show no additional buttons.
-      // Otherwise, show a "Show More" button
+      if (hasInactive) {
+        container.append(this._createShowInactiveTabsElement(client, device));
+      }
+      // If this page isn't displaying all (regular, active) tabs, show a "Show More" button.
       let hasNextPage = tabs.length > maxTabs;
       let nextPageIsLastPage =
         hasNextPage &&
@@ -248,15 +258,13 @@ this.SyncedTabsPanelList = class SyncedTabsPanelList {
         tabs = tabs.slice(0, maxTabs);
       }
       for (let [index, tab] of tabs.entries()) {
-        let tabEnt = this._createSyncedTabElement(tab, index);
-        container.appendChild(tabEnt);
-      }
-      if (numInactive) {
-        let elt = this._createShowInactiveTabsElement(
-          paginationInfo,
-          numInactive
+        let tabEnt = this._createSyncedTabElement(
+          tab,
+          index,
+          device,
+          remoteTabCloseAvailable
         );
-        container.appendChild(elt);
+        container.appendChild(tabEnt);
       }
       if (hasNextPage) {
         let showAllEnt = this._createShowMoreSyncedTabsElement(paginationInfo);
@@ -265,7 +273,10 @@ this.SyncedTabsPanelList = class SyncedTabsPanelList {
     }
   }
 
-  _createSyncedTabElement(tabInfo, index) {
+  _createSyncedTabElement(tabInfo, index, device, canCloseTabs) {
+    let tabContainer = document.createXULElement("hbox");
+    tabContainer.setAttribute("class", "PanelUI-tabitem-container");
+
     let item = document.createXULElement("toolbarbutton");
     let tooltipText = (tabInfo.title ? tabInfo.title + "\n" : "") + tabInfo.url;
     item.setAttribute("itemtype", "tab");
@@ -296,25 +307,29 @@ this.SyncedTabsPanelList = class SyncedTabsPanelList {
           {}
         ),
       });
-      if (document.defaultView.whereToOpenLink(e) != "current") {
+      if (BrowserUtils.whereToOpenLink(e) != "current") {
         e.preventDefault();
         e.stopPropagation();
       } else {
         CustomizableUI.hidePanelForNode(item);
       }
     });
-    return item;
+    tabContainer.appendChild(item);
+    // We should only add an X button next to tabs if the device
+    // is broadcasting that it can remotely close tabs
+    if (canCloseTabs) {
+      tabContainer.appendChild(
+        this._createCloseTabElement(tabInfo.url, device)
+      );
+    }
+    return tabContainer;
   }
 
   _createShowMoreSyncedTabsElement(paginationInfo) {
     let showMoreItem = document.createXULElement("toolbarbutton");
     showMoreItem.setAttribute("itemtype", "showmorebutton");
     showMoreItem.setAttribute("closemenu", "none");
-    showMoreItem.classList.add(
-      "subviewbutton",
-      "subviewbutton-nav",
-      "subviewbutton-nav-down"
-    );
+    showMoreItem.classList.add("subviewbutton", "subviewbutton-nav-down");
     document.l10n.setAttributes(showMoreItem, "appmenu-remote-tabs-showmore");
 
     paginationInfo.maxTabs = Infinity;
@@ -326,27 +341,56 @@ this.SyncedTabsPanelList = class SyncedTabsPanelList {
     return showMoreItem;
   }
 
-  _createShowInactiveTabsElement(paginationInfo, count) {
+  _createShowInactiveTabsElement(client, device) {
     let showItem = document.createXULElement("toolbarbutton");
-    showItem.setAttribute("itemtype", "showmorebutton");
     showItem.setAttribute("closemenu", "none");
-    showItem.classList.add(
-      "subviewbutton",
-      "subviewbutton-nav",
-      "subviewbutton-nav-down"
+    showItem.classList.add("subviewbutton", "subviewbutton-nav");
+    document.l10n.setAttributes(
+      showItem,
+      "appmenu-remote-tabs-show-inactive-tabs"
     );
-    document.l10n.setAttributes(showItem, "appmenu-remote-tabs-showinactive");
-    document.l10n.setArgs(showItem, { count });
 
-    paginationInfo.showInactive = true;
+    let canClose =
+      device && fxAccounts.commands.closeTab.isDeviceCompatible(device);
+
     showItem.addEventListener("click", e => {
-      e.preventDefault();
-      e.stopPropagation();
-      this._showSyncedTabs(paginationInfo);
+      let node = PanelMultiView.getViewNode(
+        document,
+        "PanelUI-fxa-menu-inactive-tabs"
+      );
+
+      // device name.
+      let label = node.querySelector("label[itemtype='client']");
+      label.textContent = client.name;
+
+      // Update the tab list.
+      let container = node.querySelector(".panel-subview-body");
+      container.replaceChildren(
+        ...client.tabs
+          .filter(t => t.inactive)
+          .map((tab, index) =>
+            this._createSyncedTabElement(tab, index, device, canClose)
+          )
+      );
+      PanelUI.showSubView("PanelUI-fxa-menu-inactive-tabs", showItem, e);
     });
     return showItem;
   }
 
+  _createCloseTabElement(url, device) {
+    let closeBtn = document.createXULElement("image");
+    closeBtn.setAttribute("class", "close-icon remotetabs-close");
+
+    closeBtn.addEventListener("click", function (e) {
+      e.stopPropagation();
+      // The user could be hitting multiple tabs across multiple devices, with a few
+      // seconds in-between -- we should not immediately fire off pushes, so we
+      // add it to a queue and send in bulk at a later time
+      fxAccounts.commands.closeTab.enqueueTabToClose(device, url);
+    });
+    return closeBtn;
+  }
+
   destroy() {
     Services.obs.removeObserver(this, SyncedTabs.TOPIC_TABS_CHANGED);
     this.tabsList = null;
@@ -384,7 +428,7 @@ var gSync = {
         "browser/accounts.ftl",
         "browser/appmenu.ftl",
         "browser/sync.ftl",
-        "toolkit/branding/accounts.ftl",
+        "browser/syncedTabs.ftl",
       ],
       true
     ));
@@ -445,7 +489,7 @@ var gSync = {
     );
     XPCOMUtils.defineLazyPreferenceGetter(
       this,
-      "PXI_TOOLBAR_ENABLED",
+      "FXA_CTA_MENU_ENABLED",
       "identity.fxaccounts.toolbar.pxiToolbarEnabled"
     );
   },
@@ -533,10 +577,23 @@ var gSync = {
     let fxaPanelView = PanelMultiView.getViewNode(document, "PanelUI-fxa");
     fxaPanelView.addEventListener("ViewShowing", this);
     fxaPanelView.addEventListener("ViewHiding", this);
+    fxaPanelView.addEventListener("command", this);
+    PanelMultiView.getViewNode(
+      document,
+      "PanelUI-fxa-menu-syncnow-button"
+    ).addEventListener("mouseover", this);
+    PanelMultiView.getViewNode(
+      document,
+      "PanelUI-fxa-menu-sendtab-not-configured-button"
+    ).addEventListener("command", this);
+    PanelMultiView.getViewNode(
+      document,
+      "PanelUI-fxa-menu-sendtab-connect-device-button"
+    ).addEventListener("command", this);
 
     // If the experiment is enabled, we'll need to update the panels
     // to show some different text to the user
-    if (this.PXI_TOOLBAR_ENABLED) {
+    if (this.FXA_CTA_MENU_ENABLED) {
       this.updateFxAPanel(UIState.get());
       this.updateCTAPanel();
     }
@@ -558,6 +615,13 @@ var gSync = {
 
   handleEvent(event) {
     switch (event.type) {
+      case "mouseover":
+        this.refreshSyncButtonsTooltip();
+        break;
+      case "command": {
+        this.onCommand(event.target);
+        break;
+      }
       case "ViewShowing": {
         this.onFxAPanelViewShowing(event.target);
         break;
@@ -606,16 +670,61 @@ var gSync = {
     panelview.syncedTabsPanelList = null;
   },
 
+  onCommand(button) {
+    switch (button.id) {
+      case "PanelUI-fxa-menu-sync-prefs-button":
+      // fall through
+      case "PanelUI-fxa-menu-setup-sync-button":
+        this.openPrefsFromFxaMenu("sync_settings", button);
+        break;
+
+      case "PanelUI-fxa-menu-sendtab-connect-device-button":
+      // fall through
+      case "PanelUI-fxa-menu-connect-device-button":
+        this.openConnectAnotherDeviceFromFxaMenu(button);
+        break;
+
+      case "fxa-manage-account-button":
+        this.clickFxAMenuHeaderButton(button);
+        break;
+      case "PanelUI-fxa-menu-syncnow-button":
+        this.doSyncFromFxaMenu(button);
+        break;
+      case "PanelUI-fxa-menu-sendtab-button":
+        this.showSendToDeviceViewFromFxaMenu(button);
+        break;
+      case "PanelUI-fxa-menu-account-signout-button":
+        this.disconnect();
+        break;
+      case "PanelUI-fxa-menu-sync-button":
+        this.openPrefsFromFxaButton("sync_cta", button);
+        break;
+      case "PanelUI-fxa-menu-monitor-button":
+        this.openMonitorLink(button);
+        break;
+      case "PanelUI-fxa-menu-relay-button":
+        this.openRelayLink(button);
+        break;
+      case "PanelUI-fxa-menu-vpn-button":
+        this.openVPNLink(button);
+        break;
+      case "PanelUI-fxa-menu-sendtab-not-configured-button":
+        this.openPrefsFromFxaMenu("send_tab", button);
+        break;
+    }
+  },
+
   observe(subject, topic, data) {
     if (!this._initialized) {
       console.error("browser-sync observer called after unload: ", topic);
       return;
     }
     switch (topic) {
-      case UIState.ON_UPDATE:
+      case UIState.ON_UPDATE: {
         const state = UIState.get();
         this.updateAllUI(state);
         break;
+      }
       case "quit-application":
         // Stop the animation timer on shutdown, since we can't update the UI
         // after this.
@@ -637,7 +746,6 @@ var gSync = {
     this.updateSyncButtonsTooltip(state);
     this.updateSyncStatus(state);
     this.updateFxAPanel(state);
-    this.updateCTAPanel(state);
     // Ensure we have something in the device list in the background.
     this.ensureFxaDevices();
   },
@@ -720,16 +828,6 @@ var gSync = {
     this.emitFxaToolbarTelemetry("send_tab", anchor);
   },
 
-  showRemoteTabsFromFxaMenu(panel) {
-    PanelUI.showSubView("PanelUI-remotetabs", panel);
-    this.emitFxaToolbarTelemetry("sync_tabs", panel);
-  },
-
-  showSidebarFromFxaMenu(panel) {
-    SidebarUI.toggle("viewTabsSidebar");
-    this.emitFxaToolbarTelemetry("sync_tabs_sidebar", panel);
-  },
-
   _populateSendTabToDevicesView(panelViewNode, reloadDevices = true) {
     let bodyNode = panelViewNode.querySelector(".panel-subview-body");
     let panelNode = panelViewNode.closest("panel");
@@ -830,12 +928,20 @@ var gSync = {
     let fxaStatus = document.documentElement.getAttribute("fxastatus");
 
     if (fxaStatus == "not_configured") {
+      // sign in button in app (hamburger) menu
+      // should take you straight to fxa sign in page
+      if (anchor.id == "appMenu-fxa-label2") {
+        this.openFxAEmailFirstPageFromFxaMenu(anchor);
+        PanelUI.hide();
+        return;
+      }
+
       // If we're signed out but have the PXI pref enabled
       // we should show the PXI panel instead of taking the user
       // straight to FxA sign-in
-      if (this.PXI_TOOLBAR_ENABLED) {
+      if (this.FXA_CTA_MENU_ENABLED) {
         this.updateFxAPanel(UIState.get());
-        this.updateCTAPanel();
+        this.updateCTAPanel(anchor);
         PanelUI.showSubView("PanelUI-fxa", anchor, aEvent);
       } else if (anchor == document.getElementById("fxa-toolbar-menu-button")) {
         // The fxa toolbar button doesn't have much context before the user
@@ -844,20 +950,13 @@ var gSync = {
         this.emitFxaToolbarTelemetry("toolbar_icon", anchor);
         openTrustedLinkIn("about:preferences#sync", "tab");
         PanelUI.hide();
-      } else {
-        let panel =
-          anchor.id == "appMenu-fxa-label2"
-            ? PanelMultiView.getViewNode(document, "PanelUI-fxa")
-            : undefined;
-        this.openFxAEmailFirstPageFromFxaMenu(panel);
-        PanelUI.hide();
       }
       return;
     }
     // If the user is signed in and we have the PXI pref enabled then add
     // the pxi panel to the existing toolbar
-    if (this.PXI_TOOLBAR_ENABLED) {
-      this.updateCTAPanel();
+    if (this.FXA_CTA_MENU_ENABLED) {
+      this.updateCTAPanel(anchor);
     }
 
     if (!gFxaToolbarAccessed) {
@@ -932,21 +1031,16 @@ var gSync = {
     fxaMenuAccountButtonEl.removeAttribute("closemenu");
     syncSetupButtonEl.removeAttribute("hidden");
 
-    let headerTitleL10nId = this.PXI_TOOLBAR_ENABLED
-      ? "appmenuitem-sign-in-account"
-      : "appmenuitem-fxa-sign-in";
+    let headerTitleL10nId = this.FXA_CTA_MENU_ENABLED
+      ? "synced-tabs-fxa-sign-in"
+      : "appmenuitem-sign-in-account";
     let headerDescription;
     if (state.status === UIState.STATUS_NOT_CONFIGURED) {
       mainWindowEl.style.removeProperty("--avatar-image-url");
-      headerDescription = this.fluentStrings.formatValueSync(
-        "appmenu-fxa-signed-in-label"
-      );
-      // Signed out, expeirment enabled is the only state we want to hide the
-      // header description, so we make it empty and check for that when setting
-      // the value
-      if (this.PXI_TOOLBAR_ENABLED) {
-        headerDescription = "";
-      }
+      const headerDescString = this.FXA_CTA_MENU_ENABLED
+        ? "fxa-menu-sync-description"
+        : "appmenu-fxa-signed-in-label";
+      headerDescription = this.fluentStrings.formatValueSync(headerDescString);
     } else if (state.status === UIState.STATUS_LOGIN_FAILED) {
       stateValue = "login-failed";
       headerTitleL10nId = "account-disconnected2";
@@ -1020,8 +1114,8 @@ var gSync = {
     ).hidden = !canSendAllURIs;
   },
 
-  emitFxaToolbarTelemetry(type, panel) {
-    if (UIState.isReady() && panel) {
+  emitFxaToolbarTelemetry(type, sourceElement) {
+    if (UIState.isReady() && sourceElement) {
       const state = UIState.get();
       const hasAvatar = state.avatarURL && !state.avatarIsDefault;
       let extraOptions = {
@@ -1029,10 +1123,10 @@ var gSync = {
         fxa_avatar: hasAvatar ? "true" : "false",
       };
 
-      // When the fxa avatar panel is within the Firefox app menu,
+      // When the source element is within the Firefox app menu,
       // we emit different telemetry.
       let eventName = "fxa_avatar_menu";
-      if (this.isPanelInsideAppMenu(panel)) {
+      if (this.isInsideAppMenu(sourceElement)) {
         eventName = "fxa_app_menu";
       }
 
@@ -1046,9 +1140,9 @@ var gSync = {
     }
   },
 
-  isPanelInsideAppMenu(panel = undefined) {
+  isInsideAppMenu(sourceElement = undefined) {
     const appMenuPanel = document.getElementById("appMenu-popup");
-    if (panel && appMenuPanel.contains(panel)) {
+    if (sourceElement && appMenuPanel.contains(sourceElement)) {
       return true;
     }
     return false;
@@ -1225,10 +1319,10 @@ var gSync = {
     openTrustedLinkIn(url, "tab");
   },
 
-  async openConnectAnotherDeviceFromFxaMenu(panel = undefined) {
-    this.emitFxaToolbarTelemetry("cad", panel);
+  async openConnectAnotherDeviceFromFxaMenu(sourceElement = undefined) {
+    this.emitFxaToolbarTelemetry("cad", sourceElement);
     let entryPoint = "fxa_discoverability_native";
-    if (this.isPanelInsideAppMenu(panel)) {
+    if (this.isInsideAppMenu(sourceElement)) {
       entryPoint = "fxa_app_menu";
     }
     this.openConnectAnotherDevice(entryPoint);
@@ -1241,7 +1335,7 @@ var gSync = {
     switchToTabHavingURI(url, true, { replaceQueryString: true });
   },
 
-  async clickFxAMenuHeaderButton(panel = undefined) {
+  async clickFxAMenuHeaderButton(sourceElement = undefined) {
     // Depending on the current logged in state of a user,
     // clicking the FxA header will either open
     // a sign-in page, account management page, or sync
@@ -1249,16 +1343,16 @@ var gSync = {
     const { status } = UIState.get();
     switch (status) {
       case UIState.STATUS_NOT_CONFIGURED:
-        this.openFxAEmailFirstPageFromFxaMenu(panel);
+        this.openFxAEmailFirstPageFromFxaMenu(sourceElement);
         break;
       case UIState.STATUS_LOGIN_FAILED:
-        this.openPrefsFromFxaMenu("sync_settings", panel);
+        this.openPrefsFromFxaMenu("sync_settings", sourceElement);
         break;
       case UIState.STATUS_NOT_VERIFIED:
         this.openFxAEmailFirstPage("fxa_app_menu_reverify");
         break;
       case UIState.STATUS_SIGNED_IN:
-        this.openFxAManagePageFromFxaMenu(panel);
+        this.openFxAManagePageFromFxaMenu(sourceElement);
     }
   },
 
@@ -1273,10 +1367,13 @@ var gSync = {
     switchToTabHavingURI(url, true, { replaceQueryString: true });
   },
 
-  async openFxAEmailFirstPageFromFxaMenu(panel = undefined, extraParams = {}) {
-    this.emitFxaToolbarTelemetry("login", panel);
+  async openFxAEmailFirstPageFromFxaMenu(
+    sourceElement = undefined,
+    extraParams = {}
+  ) {
+    this.emitFxaToolbarTelemetry("login", sourceElement);
     let entryPoint = "fxa_discoverability_native";
-    if (panel) {
+    if (sourceElement) {
       entryPoint = "fxa_toolbar_button";
     }
     this.openFxAEmailFirstPage(entryPoint, extraParams);
@@ -1287,10 +1384,10 @@ var gSync = {
     switchToTabHavingURI(url, true, { replaceQueryString: true });
   },
 
-  async openFxAManagePageFromFxaMenu(panel = undefined) {
-    this.emitFxaToolbarTelemetry("account_settings", panel);
+  async openFxAManagePageFromFxaMenu(sourceElement = undefined) {
+    this.emitFxaToolbarTelemetry("account_settings", sourceElement);
     let entryPoint = "fxa_discoverability_native";
-    if (this.isPanelInsideAppMenu(panel)) {
+    if (this.isInsideAppMenu(sourceElement)) {
       entryPoint = "fxa_app_menu";
     }
     this.openFxAManagePage(entryPoint);
@@ -1893,9 +1990,9 @@ var gSync = {
     }
   },
 
-  doSyncFromFxaMenu(panel) {
+  doSyncFromFxaMenu(sourceElement) {
     this.doSync();
-    this.emitFxaToolbarTelemetry("sync_now", panel);
+    this.emitFxaToolbarTelemetry("sync_now", sourceElement);
   },
 
   openPrefs(entryPoint = "syncbutton", origin = undefined) {
@@ -1905,18 +2002,18 @@ var gSync = {
     });
   },
 
-  openPrefsFromFxaMenu(type, panel) {
-    this.emitFxaToolbarTelemetry(type, panel);
+  openPrefsFromFxaMenu(type, sourceElement) {
+    this.emitFxaToolbarTelemetry(type, sourceElement);
     let entryPoint = "fxa_discoverability_native";
-    if (this.isPanelInsideAppMenu(panel)) {
+    if (this.isInsideAppMenu(sourceElement)) {
       entryPoint = "fxa_app_menu";
     }
     this.openPrefs(entryPoint);
   },
 
-  openPrefsFromFxaButton(type, panel) {
+  openPrefsFromFxaButton(type, sourceElement) {
     let entryPoint = "fxa_toolbar_button_sync";
-    this.emitFxaToolbarTelemetry(type, panel);
+    this.emitFxaToolbarTelemetry(type, sourceElement);
     this.openPrefs(entryPoint);
   },
 
@@ -2049,27 +2146,24 @@ var gSync = {
 
   // This should only be shown if we have enabled the pxiPanel via
   // an experiment or explicitly through prefs
-  updateCTAPanel() {
+  updateCTAPanel(anchor) {
     const mainPanelEl = PanelMultiView.getViewNode(
       document,
       "PanelUI-fxa-cta-menu"
     );
 
-    const syncCtaEl = PanelMultiView.getViewNode(
-      document,
-      "PanelUI-fxa-menu-sync-button"
-    );
-    // If we're not in the experiment then we do not enable this at all
-    if (!this.PXI_TOOLBAR_ENABLED) {
+    // If we're not in the experiment or in the app menu (hamburger)
+    // do not show this CTA panel
+    if (
+      !this.FXA_CTA_MENU_ENABLED ||
+      (anchor && anchor.id === "appMenu-fxa-label2")
+    ) {
       // If we've previously shown this but got disabled
       // we should ensure we hide the panel
       mainPanelEl.hidden = true;
       return;
     }
 
-    // If we're already signed in an syncing, we shouldn't show the sync CTA
-    syncCtaEl.hidden = this.isSignedIn;
-
     // Monitor checks
     let monitorPanelEl = PanelMultiView.getViewNode(
       document,
@@ -2112,8 +2206,8 @@ var gSync = {
       !monitorEnabled && !relayEnabled && !vpnEnabled;
     mainPanelEl.hidden = false;
   },
-  async openMonitorLink(panel) {
-    this.emitFxaToolbarTelemetry("monitor_cta", panel);
+  async openMonitorLink(sourceElement) {
+    this.emitFxaToolbarTelemetry("monitor_cta", sourceElement);
     await this.openCtaLink(
       FX_MONITOR_OAUTH_CLIENT_ID,
       new URL("https://monitor.firefox.com"),
@@ -2121,8 +2215,8 @@ var gSync = {
     );
   },
 
-  async openRelayLink(panel) {
-    this.emitFxaToolbarTelemetry("relay_cta", panel);
+  async openRelayLink(sourceElement) {
+    this.emitFxaToolbarTelemetry("relay_cta", sourceElement);
     await this.openCtaLink(
       FX_RELAY_OAUTH_CLIENT_ID,
       new URL("https://relay.firefox.com"),
@@ -2130,8 +2224,8 @@ var gSync = {
     );
   },
 
-  async openVPNLink(panel) {
-    this.emitFxaToolbarTelemetry("vpn_cta", panel);
+  async openVPNLink(sourceElement) {
+    this.emitFxaToolbarTelemetry("vpn_cta", sourceElement);
     await this.openCtaLink(
       VPN_OAUTH_CLIENT_ID,
       new URL("https://www.mozilla.org/en-US/products/vpn/"),
diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index 72753da622..5f41ca7781 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -9,6 +9,9 @@ var { XPCOMUtils } = ChromeUtils.importESModule(
 var { AppConstants } = ChromeUtils.importESModule(
   "resource://gre/modules/AppConstants.sys.mjs"
 );
+ChromeUtils.importESModule(
+  "resource://gre/modules/MemoryNotificationDB.sys.mjs"
+);
 ChromeUtils.importESModule("resource://gre/modules/NotificationDB.sys.mjs");
 
 // lazy module getters
@@ -35,8 +38,6 @@ ChromeUtils.defineESModuleGetters(this, {
   DownloadsCommon: "resource:///modules/DownloadsCommon.sys.mjs",
   E10SUtils: "resource://gre/modules/E10SUtils.sys.mjs",
   ExtensionsUI: "resource:///modules/ExtensionsUI.sys.mjs",
-  FirefoxViewNotificationManager:
-    "resource:///modules/firefox-view-notification-manager.sys.mjs",
   HomePage: "resource:///modules/HomePage.sys.mjs",
   isProductURL: "chrome://global/content/shopping/ShoppingProduct.mjs",
   LightweightThemeConsumer:
@@ -1503,1117 +1504,6 @@ function _createNullPrincipalFromTabUserContextId(tab = gBrowser.selectedTab) {
   });
 }
 
-let _resolveDelayedStartup;
-var delayedStartupPromise = new Promise(resolve => {
-  _resolveDelayedStartup = resolve;
-});
-
-var gBrowserInit = {
-  delayedStartupFinished: false,
-  idleTasksFinishedPromise: null,
-  idleTaskPromiseResolve: null,
-  domContentLoaded: false,
-
-  _tabToAdopt: undefined,
-
-  _setupFirstContentWindowPaintPromise() {
-    let lastTransactionId = window.windowUtils.lastTransactionId;
-    let layerTreeListener = () => {
-      if (this.getTabToAdopt()) {
-        // Need to wait until we finish adopting the tab, or we might end
-        // up focusing the initial browser and then losing focus when it
-        // gets swapped out for the tab to adopt.
-        return;
-      }
-      removeEventListener("MozLayerTreeReady", layerTreeListener);
-      let listener = e => {
-        if (e.transactionId > lastTransactionId) {
-          window.removeEventListener("MozAfterPaint", listener);
-          this._firstContentWindowPaintDeferred.resolve();
-        }
-      };
-      addEventListener("MozAfterPaint", listener);
-    };
-    addEventListener("MozLayerTreeReady", layerTreeListener);
-  },
-
-  getTabToAdopt() {
-    if (this._tabToAdopt !== undefined) {
-      return this._tabToAdopt;
-    }
-
-    if (window.arguments && window.XULElement.isInstance(window.arguments[0])) {
-      this._tabToAdopt = window.arguments[0];
-
-      // Clear the reference of the tab being adopted from the arguments.
-      window.arguments[0] = null;
-    } else {
-      // There was no tab to adopt in the arguments, set _tabToAdopt to null
-      // to avoid checking it again.
-      this._tabToAdopt = null;
-    }
-
-    return this._tabToAdopt;
-  },
-
-  _clearTabToAdopt() {
-    this._tabToAdopt = null;
-  },
-
-  // Used to check if the new window is still adopting an existing tab as its first tab
-  // (e.g. from the WebExtensions internals).
-  isAdoptingTab() {
-    return !!this.getTabToAdopt();
-  },
-
-  onBeforeInitialXULLayout() {
-    this._setupFirstContentWindowPaintPromise();
-
-    updateBookmarkToolbarVisibility();
-
-    // Set a sane starting width/height for all resolutions on new profiles.
-    if (ChromeUtils.shouldResistFingerprinting("RoundWindowSize", null)) {
-      // When the fingerprinting resistance is enabled, making sure that we don't
-      // have a maximum window to interfere with generating rounded window dimensions.
-      document.documentElement.setAttribute("sizemode", "normal");
-    } else if (!document.documentElement.hasAttribute("width")) {
-      const TARGET_WIDTH = 1280;
-      const TARGET_HEIGHT = 1040;
-      let width = Math.min(screen.availWidth * 0.9, TARGET_WIDTH);
-      let height = Math.min(screen.availHeight * 0.9, TARGET_HEIGHT);
-
-      document.documentElement.setAttribute("width", width);
-      document.documentElement.setAttribute("height", height);
-
-      if (width < TARGET_WIDTH && height < TARGET_HEIGHT) {
-        document.documentElement.setAttribute("sizemode", "maximized");
-      }
-    }
-    if (AppConstants.MENUBAR_CAN_AUTOHIDE) {
-      const toolbarMenubar = document.getElementById("toolbar-menubar");
-      // set a default value
-      if (!toolbarMenubar.hasAttribute("autohide")) {
-        toolbarMenubar.setAttribute("autohide", true);
-      }
-      document.l10n.setAttributes(
-        toolbarMenubar,
-        "toolbar-context-menu-menu-bar-cmd"
-      );
-      toolbarMenubar.setAttribute("data-l10n-attrs", "toolbarname");
-    }
-
-    // Run menubar initialization first, to avoid TabsInTitlebar code picking
-    // up mutations from it and causing a reflow.
-    AutoHideMenubar.init();
-    // Update the chromemargin attribute so the window can be sized correctly.
-    window.TabBarVisibility.update();
-    TabsInTitlebar.init();
-
-    new LightweightThemeConsumer(document);
-
-    if (
-      Services.prefs.getBoolPref(
-        "toolkit.legacyUserProfileCustomizations.windowIcon",
-        false
-      )
-    ) {
-      document.documentElement.setAttribute("icon", "main-window");
-    }
-
-    // Call this after we set attributes that might change toolbars' computed
-    // text color.
-    ToolbarIconColor.init();
-  },
-
-  onDOMContentLoaded() {
-    // This needs setting up before we create the first remote browser.
-    window.docShell.treeOwner
-      .QueryInterface(Ci.nsIInterfaceRequestor)
-      .getInterface(Ci.nsIAppWindow).XULBrowserWindow = window.XULBrowserWindow;
-    window.browserDOMWindow = new nsBrowserAccess();
-
-    gBrowser = window._gBrowser;
-    delete window._gBrowser;
-    gBrowser.init();
-
-    BrowserWindowTracker.track(window);
-
-    FirefoxViewHandler.init();
-
-    gNavToolbox.palette = document.getElementById(
-      "BrowserToolbarPalette"
-    ).content;
-    for (let area of CustomizableUI.areas) {
-      let type = CustomizableUI.getAreaType(area);
-      if (type == CustomizableUI.TYPE_TOOLBAR) {
-        let node = document.getElementById(area);
-        CustomizableUI.registerToolbarNode(node);
-      }
-    }
-    BrowserSearch.initPlaceHolder();
-
-    // Hack to ensure that the various initial pages favicon is loaded
-    // instantaneously, to avoid flickering and improve perceived performance.
-    this._callWithURIToLoad(uriToLoad => {
-      let url;
-      try {
-        url = Services.io.newURI(uriToLoad);
-      } catch (e) {
-        return;
-      }
-      let nonQuery = url.prePath + url.filePath;
-      if (nonQuery in gPageIcons) {
-        gBrowser.setIcon(gBrowser.selectedTab, gPageIcons[nonQuery]);
-      }
-    });
-
-    updateFxaToolbarMenu(gFxaToolbarEnabled, true);
-
-    updatePrintCommands(gPrintEnabled);
-
-    gUnifiedExtensions.init();
-
-    // Setting the focus will cause a style flush, it's preferable to call anything
-    // that will modify the DOM from within this function before this call.
-    this._setInitialFocus();
-
-    this.domContentLoaded = true;
-  },
-
-  onLoad() {
-    gBrowser.addEventListener("DOMUpdateBlockedPopups", gPopupBlockerObserver);
-    gBrowser.addEventListener(
-      "TranslationsParent:LanguageState",
-      FullPageTranslationsPanel
-    );
-    gBrowser.addEventListener(
-      "TranslationsParent:OfferTranslation",
-      FullPageTranslationsPanel
-    );
-    gBrowser.addTabsProgressListener(FullPageTranslationsPanel);
-
-    window.addEventListener("AppCommand", HandleAppCommandEvent, true);
-
-    // These routines add message listeners. They must run before
-    // loading the frame script to ensure that we don't miss any
-    // message sent between when the frame script is loaded and when
-    // the listener is registered.
-    CaptivePortalWatcher.init();
-    ZoomUI.init(window);
-
-    if (!gMultiProcessBrowser) {
-      // There is a Content:Click message manually sent from content.
-      gBrowser.tabpanels.addEventListener("click", contentAreaClick, {
-        capture: true,
-        mozSystemGroup: true,
-      });
-    }
-
-    // hook up UI through progress listener
-    gBrowser.addProgressListener(window.XULBrowserWindow);
-    gBrowser.addTabsProgressListener(window.TabsProgressListener);
-
-    SidebarUI.init();
-
-    // We do this in onload because we want to ensure the button's state
-    // doesn't flicker as the window is being shown.
-    DownloadsButton.init();
-
-    // Certain kinds of automigration rely on this notification to complete
-    // their tasks BEFORE the browser window is shown. SessionStore uses it to
-    // restore tabs into windows AFTER important parts like gMultiProcessBrowser
-    // have been initialized.
-    Services.obs.notifyObservers(window, "browser-window-before-show");
-
-    if (!window.toolbar.visible) {
-      // adjust browser UI for popups
-      gURLBar.readOnly = true;
-    }
-
-    // Misc. inits.
-    gUIDensity.init();
-    TabletModeUpdater.init();
-    CombinedStopReload.ensureInitialized();
-    gPrivateBrowsingUI.init();
-    BrowserSearch.init();
-    BrowserPageActions.init();
-    if (gToolbarKeyNavEnabled) {
-      ToolbarKeyboardNavigator.init();
-    }
-
-    // Update UI if browser is under remote control.
-    gRemoteControl.updateVisualCue();
-
-    // If we are given a tab to swap in, take care of it before first paint to
-    // avoid an about:blank flash.
-    let tabToAdopt = this.getTabToAdopt();
-    if (tabToAdopt) {
-      let evt = new CustomEvent("before-initial-tab-adopted", {
-        bubbles: true,
-      });
-      gBrowser.tabpanels.dispatchEvent(evt);
-
-      // Stop the about:blank load
-      gBrowser.stop();
-
-      // Remove the speculative focus from the urlbar to let the url be formatted.
-      gURLBar.removeAttribute("focused");
-
-      let swapBrowsers = () => {
-        try {
-          gBrowser.swapBrowsersAndCloseOther(gBrowser.selectedTab, tabToAdopt);
-        } catch (e) {
-          console.error(e);
-        }
-
-        // Clear the reference to the tab once its adoption has been completed.
-        this._clearTabToAdopt();
-      };
-      if (tabToAdopt.linkedBrowser.isRemoteBrowser) {
-        // For remote browsers, wait for the paint event, otherwise the tabs
-        // are not yet ready and focus gets confused because the browser swaps
-        // out while tabs are switching.
-        addEventListener("MozAfterPaint", swapBrowsers, { once: true });
-      } else {
-        swapBrowsers();
-      }
-    }
-
-    // Wait until chrome is painted before executing code not critical to making the window visible
-    this._boundDelayedStartup = this._delayedStartup.bind(this);
-    window.addEventListener("MozAfterPaint", this._boundDelayedStartup);
-
-    if (!PrivateBrowsingUtils.enabled) {
-      document.getElementById("Tools:PrivateBrowsing").hidden = true;
-      // Setting disabled doesn't disable the shortcut, so we just remove
-      // the keybinding.
-      document.getElementById("key_privatebrowsing").remove();
-    }
-
-    if (BrowserUIUtils.quitShortcutDisabled) {
-      document.getElementById("key_quitApplication").remove();
-      document.getElementById("menu_FileQuitItem").removeAttribute("key");
-
-      PanelMultiView.getViewNode(
-        document,
-        "appMenu-quit-button2"
-      )?.removeAttribute("key");
-    }
-
-    this._loadHandled = true;
-  },
-
-  _cancelDelayedStartup() {
-    window.removeEventListener("MozAfterPaint", this._boundDelayedStartup);
-    this._boundDelayedStartup = null;
-  },
-
-  _delayedStartup() {
-    let { TelemetryTimestamps } = ChromeUtils.importESModule(
-      "resource://gre/modules/TelemetryTimestamps.sys.mjs"
-    );
-    TelemetryTimestamps.add("delayedStartupStarted");
-
-    this._cancelDelayedStartup();
-
-    // Bug 1531854 - The hidden window is force-created here
-    // until all of its dependencies are handled.
-    Services.appShell.hiddenDOMWindow;
-
-    gBrowser.addEventListener(
-      "PermissionStateChange",
-      function () {
-        gIdentityHandler.refreshIdentityBlock();
-        gPermissionPanel.updateSharingIndicator();
-      },
-      true
-    );
-
-    this._handleURIToLoad();
-
-    Services.obs.addObserver(gIdentityHandler, "perm-changed");
-    Services.obs.addObserver(gRemoteControl, "devtools-socket");
-    Services.obs.addObserver(gRemoteControl, "marionette-listening");
-    Services.obs.addObserver(gRemoteControl, "remote-listening");
-    Services.obs.addObserver(
-      gSessionHistoryObserver,
-      "browser:purge-session-history"
-    );
-    Services.obs.addObserver(
-      gStoragePressureObserver,
-      "QuotaManager::StoragePressure"
-    );
-    Services.obs.addObserver(gXPInstallObserver, "addon-install-disabled");
-    Services.obs.addObserver(gXPInstallObserver, "addon-install-started");
-    Services.obs.addObserver(gXPInstallObserver, "addon-install-blocked");
-    Services.obs.addObserver(
-      gXPInstallObserver,
-      "addon-install-fullscreen-blocked"
-    );
-    Services.obs.addObserver(
-      gXPInstallObserver,
-      "addon-install-origin-blocked"
-    );
-    Services.obs.addObserver(
-      gXPInstallObserver,
-      "addon-install-policy-blocked"
-    );
-    Services.obs.addObserver(
-      gXPInstallObserver,
-      "addon-install-webapi-blocked"
-    );
-    Services.obs.addObserver(gXPInstallObserver, "addon-install-failed");
-    Services.obs.addObserver(gXPInstallObserver, "addon-install-confirmation");
-    Services.obs.addObserver(gKeywordURIFixup, "keyword-uri-fixup");
-
-    BrowserOffline.init();
-    CanvasPermissionPromptHelper.init();
-    WebAuthnPromptHelper.init();
-    ContentAnalysis.initialize();
-
-    // Initialize the full zoom setting.
-    // We do this before the session restore service gets initialized so we can
-    // apply full zoom settings to tabs restored by the session restore service.
-    FullZoom.init();
-    PanelUI.init(shouldSuppressPopupNotifications);
-    ReportBrokenSite.init(gBrowser);
-
-    UpdateUrlbarSearchSplitterState();
-
-    BookmarkingUI.init();
-    BrowserSearch.delayedStartupInit();
-    SearchUIUtils.init();
-    gProtectionsHandler.init();
-    HomePage.delayedStartup().catch(console.error);
-
-    let safeMode = document.getElementById("helpSafeMode");
-    if (Services.appinfo.inSafeMode) {
-      document.l10n.setAttributes(safeMode, "menu-help-exit-troubleshoot-mode");
-      safeMode.setAttribute(
-        "appmenu-data-l10n-id",
-        "appmenu-help-exit-troubleshoot-mode"
-      );
-    }
-
-    // BiDi UI
-    gBidiUI = isBidiEnabled();
-    if (gBidiUI) {
-      document.getElementById("documentDirection-separator").hidden = false;
-      document.getElementById("documentDirection-swap").hidden = false;
-      document.getElementById("textfieldDirection-separator").hidden = false;
-      document.getElementById("textfieldDirection-swap").hidden = false;
-    }
-
-    // Setup click-and-hold gestures access to the session history
-    // menus if global click-and-hold isn't turned on
-    if (!Services.prefs.getBoolPref("ui.click_hold_context_menus", false)) {
-      SetClickAndHoldHandlers();
-    }
-
-    function initBackForwardButtonTooltip(tooltipId, l10nId, shortcutId) {
-      let shortcut = document.getElementById(shortcutId);
-      shortcut = ShortcutUtils.prettifyShortcut(shortcut);
-
-      let tooltip = document.getElementById(tooltipId);
-      document.l10n.setAttributes(tooltip, l10nId, { shortcut });
-    }
-
-    initBackForwardButtonTooltip(
-      "back-button-tooltip-description",
-      "navbar-tooltip-back-2",
-      "goBackKb"
-    );
-
-    initBackForwardButtonTooltip(
-      "forward-button-tooltip-description",
-      "navbar-tooltip-forward-2",
-      "goForwardKb"
-    );
-
-    PlacesToolbarHelper.init();
-
-    ctrlTab.readPref();
-    Services.prefs.addObserver(ctrlTab.prefName, ctrlTab);
-
-    // The object handling the downloads indicator is initialized here in the
-    // delayed startup function, but the actual indicator element is not loaded
-    // unless there are downloads to be displayed.
-    DownloadsButton.initializeIndicator();
-
-    if (AppConstants.platform != "macosx") {
-      updateEditUIVisibility();
-      let placesContext = document.getElementById("placesContext");
-      placesContext.addEventListener("popupshowing", updateEditUIVisibility);
-      placesContext.addEventListener("popuphiding", updateEditUIVisibility);
-    }
-
-    FullScreen.init();
-    MenuTouchModeObserver.init();
-
-    if (AppConstants.MOZ_DATA_REPORTING) {
-      gDataNotificationInfoBar.init();
-    }
-
-    if (!AppConstants.MOZILLA_OFFICIAL) {
-      DevelopmentHelpers.init();
-    }
-
-    gExtensionsNotifications.init();
-
-    let wasMinimized = window.windowState == window.STATE_MINIMIZED;
-    window.addEventListener("sizemodechange", () => {
-      let isMinimized = window.windowState == window.STATE_MINIMIZED;
-      if (wasMinimized != isMinimized) {
-        wasMinimized = isMinimized;
-        UpdatePopupNotificationsVisibility();
-      }
-    });
-
-    window.addEventListener("mousemove", MousePosTracker);
-    window.addEventListener("dragover", MousePosTracker);
-
-    gNavToolbox.addEventListener("customizationstarting", CustomizationHandler);
-    gNavToolbox.addEventListener("aftercustomization", CustomizationHandler);
-
-    SessionStore.promiseInitialized.then(() => {
-      // Bail out if the window has been closed in the meantime.
-      if (window.closed) {
-        return;
-      }
-
-      // Enable the Restore Last Session command if needed
-      RestoreLastSessionObserver.init();
-
-      SidebarUI.startDelayedLoad();
-
-      PanicButtonNotifier.init();
-    });
-
-    if (BrowserHandler.kiosk) {
-      // We don't modify popup windows for kiosk mode
-      if (!gURLBar.readOnly) {
-        window.fullScreen = true;
-      }
-    }
-
-    if (Services.policies.status === Services.policies.ACTIVE) {
-      if (!Services.policies.isAllowed("hideShowMenuBar")) {
-        document
-          .getElementById("toolbar-menubar")
-          .removeAttribute("toolbarname");
-      }
-      if (!Services.policies.isAllowed("filepickers")) {
-        let savePageCommand = document.getElementById("Browser:SavePage");
-        let openFileCommand = document.getElementById("Browser:OpenFile");
-
-        savePageCommand.setAttribute("disabled", "true");
-        openFileCommand.setAttribute("disabled", "true");
-
-        document.addEventListener("FilePickerBlocked", function (event) {
-          let browser = event.target;
-
-          let notificationBox = browser
-            .getTabBrowser()
-            ?.getNotificationBox(browser);
-
-          // Prevent duplicate notifications
-          if (
-            notificationBox &&
-            !notificationBox.getNotificationWithValue("filepicker-blocked")
-          ) {
-            notificationBox.appendNotification("filepicker-blocked", {
-              label: {
-                "l10n-id": "filepicker-blocked-infobar",
-              },
-              priority: notificationBox.PRIORITY_INFO_LOW,
-            });
-          }
-        });
-      }
-      let policies = Services.policies.getActivePolicies();
-      if ("ManagedBookmarks" in policies) {
-        let managedBookmarks = policies.ManagedBookmarks;
-        let children = managedBookmarks.filter(
-          child => !("toplevel_name" in child)
-        );
-        if (children.length) {
-          let managedBookmarksButton =
-            document.createXULElement("toolbarbutton");
-          managedBookmarksButton.setAttribute("id", "managed-bookmarks");
-          managedBookmarksButton.setAttribute("class", "bookmark-item");
-          let toplevel = managedBookmarks.find(
-            element => "toplevel_name" in element
-          );
-          if (toplevel) {
-            managedBookmarksButton.setAttribute(
-              "label",
-              toplevel.toplevel_name
-            );
-          } else {
-            document.l10n.setAttributes(
-              managedBookmarksButton,
-              "managed-bookmarks"
-            );
-          }
-          managedBookmarksButton.setAttribute("context", "placesContext");
-          managedBookmarksButton.setAttribute("container", "true");
-          managedBookmarksButton.setAttribute("removable", "false");
-          managedBookmarksButton.setAttribute("type", "menu");
-
-          let managedBookmarksPopup = document.createXULElement("menupopup");
-          managedBookmarksPopup.setAttribute("id", "managed-bookmarks-popup");
-          managedBookmarksPopup.setAttribute(
-            "oncommand",
-            "PlacesToolbarHelper.openManagedBookmark(event);"
-          );
-          managedBookmarksPopup.setAttribute(
-            "ondragover",
-            "event.dataTransfer.effectAllowed='none';"
-          );
-          managedBookmarksPopup.setAttribute(
-            "ondragstart",
-            "PlacesToolbarHelper.onDragStartManaged(event);"
-          );
-          managedBookmarksPopup.setAttribute(
-            "onpopupshowing",
-            "PlacesToolbarHelper.populateManagedBookmarks(this);"
-          );
-          managedBookmarksPopup.setAttribute("placespopup", "true");
-          managedBookmarksPopup.setAttribute("is", "places-popup");
-          managedBookmarksPopup.classList.add("toolbar-menupopup");
-          managedBookmarksButton.appendChild(managedBookmarksPopup);
-
-          gNavToolbox.palette.appendChild(managedBookmarksButton);
-
-          CustomizableUI.ensureWidgetPlacedInWindow(
-            "managed-bookmarks",
-            window
-          );
-
-          // Add button if it doesn't exist
-          if (!CustomizableUI.getPlacementOfWidget("managed-bookmarks")) {
-            CustomizableUI.addWidgetToArea(
-              "managed-bookmarks",
-              CustomizableUI.AREA_BOOKMARKS,
-              0
-            );
-          }
-        }
-      }
-    }
-
-    CaptivePortalWatcher.delayedStartup();
-
-    ShoppingSidebarManager.ensureInitialized();
-
-    SessionStore.promiseAllWindowsRestored.then(() => {
-      this._schedulePerWindowIdleTasks();
-      document.documentElement.setAttribute("sessionrestored", "true");
-    });
-
-    this.delayedStartupFinished = true;
-    _resolveDelayedStartup();
-    Services.obs.notifyObservers(window, "browser-delayed-startup-finished");
-    TelemetryTimestamps.add("delayedStartupFinished");
-    // We've announced that delayed startup has finished. Do not add code past this point.
-  },
-
-  /**
-   * Resolved on the first MozLayerTreeReady and next MozAfterPaint in the
-   * parent process.
-   */
-  get firstContentWindowPaintPromise() {
-    return this._firstContentWindowPaintDeferred.promise;
-  },
-
-  _setInitialFocus() {
-    let initiallyFocusedElement = document.commandDispatcher.focusedElement;
-
-    // To prevent startup flicker, the urlbar has the 'focused' attribute set
-    // by default. If we are not sure the urlbar will be focused in this
-    // window, we need to remove the attribute before first paint.
-    // TODO (bug 1629956): The urlbar having the 'focused' attribute by default
-    // isn't a useful optimization anymore since UrlbarInput needs layout
-    // information to focus the urlbar properly.
-    let shouldRemoveFocusedAttribute = true;
-
-    this._callWithURIToLoad(uriToLoad => {
-      if (
-        isBlankPageURL(uriToLoad) ||
-        uriToLoad == "about:privatebrowsing" ||
-        this.getTabToAdopt()?.isEmpty
-      ) {
-        gURLBar.select();
-        shouldRemoveFocusedAttribute = false;
-        return;
-      }
-
-      // If the initial browser is remote, in order to optimize for first paint,
-      // we'll defer switching focus to that browser until it has painted.
-      // Otherwise use a regular promise to guarantee that mutationobserver
-      // microtasks that could affect focusability have run.
-      let promise = gBrowser.selectedBrowser.isRemoteBrowser
-        ? this.firstContentWindowPaintPromise
-        : Promise.resolve();
-
-      promise.then(() => {
-        // If focus didn't move while we were waiting, we're okay to move to
-        // the browser.
-        if (
-          document.commandDispatcher.focusedElement == initiallyFocusedElement
-        ) {
-          gBrowser.selectedBrowser.focus();
-        }
-      });
-    });
-
-    // Delay removing the attribute using requestAnimationFrame to avoid
-    // invalidating styles multiple times in a row if uriToLoadPromise
-    // resolves before first paint.
-    if (shouldRemoveFocusedAttribute) {
-      window.requestAnimationFrame(() => {
-        if (shouldRemoveFocusedAttribute) {
-          gURLBar.removeAttribute("focused");
-        }
-      });
-    }
-  },
-
-  _handleURIToLoad() {
-    this._callWithURIToLoad(uriToLoad => {
-      if (!uriToLoad) {
-        // We don't check whether window.arguments[5] (userContextId) is set
-        // because tabbrowser.js takes care of that for the initial tab.
-        return;
-      }
-
-      // We don't check if uriToLoad is a XULElement because this case has
-      // already been handled before first paint, and the argument cleared.
-      if (Array.isArray(uriToLoad)) {
-        // This function throws for certain malformed URIs, so use exception handling
-        // so that we don't disrupt startup
-        try {
-          gBrowser.loadTabs(uriToLoad, {
-            inBackground: false,
-            replace: true,
-            // See below for the semantics of window.arguments. Only the minimum is supported.
-            userContextId: window.arguments[5],
-            triggeringPrincipal:
-              window.arguments[8] ||
-              Services.scriptSecurityManager.getSystemPrincipal(),
-            allowInheritPrincipal: window.arguments[9],
-            csp: window.arguments[10],
-            fromExternal: true,
-          });
-        } catch (e) {}
-      } else if (window.arguments.length >= 3) {
-        // window.arguments[1]: extraOptions (nsIPropertyBag)
-        //                 [2]: referrerInfo (nsIReferrerInfo)
-        //                 [3]: postData (nsIInputStream)
-        //                 [4]: allowThirdPartyFixup (bool)
-        //                 [5]: userContextId (int)
-        //                 [6]: originPrincipal (nsIPrincipal)
-        //                 [7]: originStoragePrincipal (nsIPrincipal)
-        //                 [8]: triggeringPrincipal (nsIPrincipal)
-        //                 [9]: allowInheritPrincipal (bool)
-        //                 [10]: csp (nsIContentSecurityPolicy)
-        //                 [11]: nsOpenWindowInfo
-        let userContextId =
-          window.arguments[5] != undefined
-            ? window.arguments[5]
-            : Ci.nsIScriptSecurityManager.DEFAULT_USER_CONTEXT_ID;
-
-        let hasValidUserGestureActivation = undefined;
-        let fromExternal = undefined;
-        let globalHistoryOptions = undefined;
-        let triggeringRemoteType = undefined;
-        let forceAllowDataURI = false;
-        let wasSchemelessInput = false;
-        if (window.arguments[1]) {
-          if (!(window.arguments[1] instanceof Ci.nsIPropertyBag2)) {
-            throw new Error(
-              "window.arguments[1] must be null or Ci.nsIPropertyBag2!"
-            );
-          }
-
-          let extraOptions = window.arguments[1];
-          if (extraOptions.hasKey("hasValidUserGestureActivation")) {
-            hasValidUserGestureActivation = extraOptions.getPropertyAsBool(
-              "hasValidUserGestureActivation"
-            );
-          }
-          if (extraOptions.hasKey("fromExternal")) {
-            fromExternal = extraOptions.getPropertyAsBool("fromExternal");
-          }
-          if (extraOptions.hasKey("triggeringSponsoredURL")) {
-            globalHistoryOptions = {
-              triggeringSponsoredURL: extraOptions.getPropertyAsACString(
-                "triggeringSponsoredURL"
-              ),
-            };
-            if (extraOptions.hasKey("triggeringSponsoredURLVisitTimeMS")) {
-              globalHistoryOptions.triggeringSponsoredURLVisitTimeMS =
-                extraOptions.getPropertyAsUint64(
-                  "triggeringSponsoredURLVisitTimeMS"
-                );
-            }
-          }
-          if (extraOptions.hasKey("triggeringRemoteType")) {
-            triggeringRemoteType = extraOptions.getPropertyAsACString(
-              "triggeringRemoteType"
-            );
-          }
-          if (extraOptions.hasKey("forceAllowDataURI")) {
-            forceAllowDataURI =
-              extraOptions.getPropertyAsBool("forceAllowDataURI");
-          }
-          if (extraOptions.hasKey("wasSchemelessInput")) {
-            wasSchemelessInput =
-              extraOptions.getPropertyAsBool("wasSchemelessInput");
-          }
-        }
-
-        try {
-          openLinkIn(uriToLoad, "current", {
-            referrerInfo: window.arguments[2] || null,
-            postData: window.arguments[3] || null,
-            allowThirdPartyFixup: window.arguments[4] || false,
-            userContextId,
-            // pass the origin principal (if any) and force its use to create
-            // an initial about:blank viewer if present:
-            originPrincipal: window.arguments[6],
-            originStoragePrincipal: window.arguments[7],
-            triggeringPrincipal: window.arguments[8],
-            // TODO fix allowInheritPrincipal to default to false.
-            // Default to true unless explicitly set to false because of bug 1475201.
-            allowInheritPrincipal: window.arguments[9] !== false,
-            csp: window.arguments[10],
-            forceAboutBlankViewerInCurrent: !!window.arguments[6],
-            forceAllowDataURI,
-            hasValidUserGestureActivation,
-            fromExternal,
-            globalHistoryOptions,
-            triggeringRemoteType,
-            wasSchemelessInput,
-          });
-        } catch (e) {
-          console.error(e);
-        }
-
-        window.focus();
-      } else {
-        // Note: loadOneOrMoreURIs *must not* be called if window.arguments.length >= 3.
-        // Such callers expect that window.arguments[0] is handled as a single URI.
-        loadOneOrMoreURIs(
-          uriToLoad,
-          Services.scriptSecurityManager.getSystemPrincipal(),
-          null
-        );
-      }
-    });
-  },
-
-  /**
-   * Use this function as an entry point to schedule tasks that
-   * need to run once per window after startup, and can be scheduled
-   * by using an idle callback.
-   *
-   * The functions scheduled here will fire from idle callbacks
-   * once every window has finished being restored by session
-   * restore, and after the equivalent only-once tasks
-   * have run (from _scheduleStartupIdleTasks in BrowserGlue.sys.mjs).
-   */
-  _schedulePerWindowIdleTasks() {
-    // Bail out if the window has been closed in the meantime.
-    if (window.closed) {
-      return;
-    }
-
-    function scheduleIdleTask(func, options) {
-      requestIdleCallback(function idleTaskRunner() {
-        if (!window.closed) {
-          func();
-        }
-      }, options);
-    }
-
-    scheduleIdleTask(() => {
-      // Initialize the Sync UI
-      gSync.init();
-    });
-
-    scheduleIdleTask(() => {
-      // Read prefers-reduced-motion setting
-      let reduceMotionQuery = window.matchMedia(
-        "(prefers-reduced-motion: reduce)"
-      );
-      function readSetting() {
-        gReduceMotionSetting = reduceMotionQuery.matches;
-      }
-      reduceMotionQuery.addListener(readSetting);
-      readSetting();
-    });
-
-    scheduleIdleTask(() => {
-      // setup simple gestures support
-      gGestureSupport.init(true);
-
-      // setup history swipe animation
-      gHistorySwipeAnimation.init();
-    });
-
-    scheduleIdleTask(() => {
-      gBrowserThumbnails.init();
-    });
-
-    scheduleIdleTask(
-      () => {
-        // Initialize the download manager some time after the app starts so that
-        // auto-resume downloads begin (such as after crashing or quitting with
-        // active downloads) and speeds up the first-load of the download manager UI.
-        // If the user manually opens the download manager before the timeout, the
-        // downloads will start right away, and initializing again won't hurt.
-        try {
-          DownloadsCommon.initializeAllDataLinks();
-          ChromeUtils.importESModule(
-            "resource:///modules/DownloadsTaskbar.sys.mjs"
-          ).DownloadsTaskbar.registerIndicator(window);
-          if (AppConstants.platform == "macosx") {
-            ChromeUtils.importESModule(
-              "resource:///modules/DownloadsMacFinderProgress.sys.mjs"
-            ).DownloadsMacFinderProgress.register();
-          }
-          Services.telemetry.setEventRecordingEnabled("downloads", true);
-        } catch (ex) {
-          console.error(ex);
-        }
-      },
-      { timeout: 10000 }
-    );
-
-    if (Win7Features) {
-      scheduleIdleTask(() => Win7Features.onOpenWindow());
-    }
-
-    scheduleIdleTask(async () => {
-      NewTabPagePreloading.maybeCreatePreloadedBrowser(window);
-    });
-
-    scheduleIdleTask(() => {
-      gGfxUtils.init();
-    });
-
-    // This should always go last, since the idle tasks (except for the ones with
-    // timeouts) should execute in order. Note that this observer notification is
-    // not guaranteed to fire, since the window could close before we get here.
-    scheduleIdleTask(() => {
-      this.idleTaskPromiseResolve();
-      Services.obs.notifyObservers(
-        window,
-        "browser-idle-startup-tasks-finished"
-      );
-    });
-
-    scheduleIdleTask(() => {
-      gProfiles.init();
-    });
-  },
-
-  // Returns the URI(s) to load at startup if it is immediately known, or a
-  // promise resolving to the URI to load.
-  get uriToLoadPromise() {
-    delete this.uriToLoadPromise;
-    return (this.uriToLoadPromise = (function () {
-      // window.arguments[0]: URI to load (string), or an nsIArray of
-      //                      nsISupportsStrings to load, or a xul:tab of
-      //                      a tabbrowser, which will be replaced by this
-      //                      window (for this case, all other arguments are
-      //                      ignored).
-      let uri = window.arguments?.[0];
-      if (!uri || window.XULElement.isInstance(uri)) {
-        return null;
-      }
-
-      let defaultArgs = BrowserHandler.defaultArgs;
-
-      // If the given URI is different from the homepage, we want to load it.
-      if (uri != defaultArgs) {
-        AboutNewTab.noteNonDefaultStartup();
-
-        if (uri instanceof Ci.nsIArray) {
-          // Transform the nsIArray of nsISupportsString's into a JS Array of
-          // JS strings.
-          return Array.from(
-            uri.enumerate(Ci.nsISupportsString),
-            supportStr => supportStr.data
-          );
-        } else if (uri instanceof Ci.nsISupportsString) {
-          return uri.data;
-        }
-        return uri;
-      }
-
-      // The URI appears to be the the homepage. We want to load it only if
-      // session restore isn't about to override the homepage.
-      let willOverride = SessionStartup.willOverrideHomepage;
-      if (typeof willOverride == "boolean") {
-        return willOverride ? null : uri;
-      }
-      return willOverride.then(willOverrideHomepage =>
-        willOverrideHomepage ? null : uri
-      );
-    })());
-  },
-
-  // Calls the given callback with the URI to load at startup.
-  // Synchronously if possible, or after uriToLoadPromise resolves otherwise.
-  _callWithURIToLoad(callback) {
-    let uriToLoad = this.uriToLoadPromise;
-    if (uriToLoad && uriToLoad.then) {
-      uriToLoad.then(callback);
-    } else {
-      callback(uriToLoad);
-    }
-  },
-
-  onUnload() {
-    gUIDensity.uninit();
-
-    TabsInTitlebar.uninit();
-
-    ToolbarIconColor.uninit();
-
-    // In certain scenarios it's possible for unload to be fired before onload,
-    // (e.g. if the window is being closed after browser.js loads but before the
-    // load completes). In that case, there's nothing to do here.
-    if (!this._loadHandled) {
-      return;
-    }
-
-    // First clean up services initialized in gBrowserInit.onLoad (or those whose
-    // uninit methods don't depend on the services having been initialized).
-
-    CombinedStopReload.uninit();
-
-    gGestureSupport.init(false);
-
-    gHistorySwipeAnimation.uninit();
-
-    FullScreen.uninit();
-
-    gSync.uninit();
-
-    gExtensionsNotifications.uninit();
-    gUnifiedExtensions.uninit();
-
-    try {
-      gBrowser.removeProgressListener(window.XULBrowserWindow);
-      gBrowser.removeTabsProgressListener(window.TabsProgressListener);
-    } catch (ex) {}
-
-    PlacesToolbarHelper.uninit();
-
-    BookmarkingUI.uninit();
-
-    TabletModeUpdater.uninit();
-
-    gTabletModePageCounter.finish();
-
-    CaptivePortalWatcher.uninit();
-
-    SidebarUI.uninit();
-
-    DownloadsButton.uninit();
-
-    if (gToolbarKeyNavEnabled) {
-      ToolbarKeyboardNavigator.uninit();
-    }
-
-    BrowserSearch.uninit();
-
-    NewTabPagePreloading.removePreloadedBrowser(window);
-
-    FirefoxViewHandler.uninit();
-
-    // Now either cancel delayedStartup, or clean up the services initialized from
-    // it.
-    if (this._boundDelayedStartup) {
-      this._cancelDelayedStartup();
-    } else {
-      if (Win7Features) {
-        Win7Features.onCloseWindow();
-      }
-      Services.prefs.removeObserver(ctrlTab.prefName, ctrlTab);
-      ctrlTab.uninit();
-      gBrowserThumbnails.uninit();
-      gProtectionsHandler.uninit();
-      FullZoom.destroy();
-
-      Services.obs.removeObserver(gIdentityHandler, "perm-changed");
-      Services.obs.removeObserver(gRemoteControl, "devtools-socket");
-      Services.obs.removeObserver(gRemoteControl, "marionette-listening");
-      Services.obs.removeObserver(gRemoteControl, "remote-listening");
-      Services.obs.removeObserver(
-        gSessionHistoryObserver,
-        "browser:purge-session-history"
-      );
-      Services.obs.removeObserver(
-        gStoragePressureObserver,
-        "QuotaManager::StoragePressure"
-      );
-      Services.obs.removeObserver(gXPInstallObserver, "addon-install-disabled");
-      Services.obs.removeObserver(gXPInstallObserver, "addon-install-started");
-      Services.obs.removeObserver(gXPInstallObserver, "addon-install-blocked");
-      Services.obs.removeObserver(
-        gXPInstallObserver,
-        "addon-install-fullscreen-blocked"
-      );
-      Services.obs.removeObserver(
-        gXPInstallObserver,
-        "addon-install-origin-blocked"
-      );
-      Services.obs.removeObserver(
-        gXPInstallObserver,
-        "addon-install-policy-blocked"
-      );
-      Services.obs.removeObserver(
-        gXPInstallObserver,
-        "addon-install-webapi-blocked"
-      );
-      Services.obs.removeObserver(gXPInstallObserver, "addon-install-failed");
-      Services.obs.removeObserver(
-        gXPInstallObserver,
-        "addon-install-confirmation"
-      );
-      Services.obs.removeObserver(gKeywordURIFixup, "keyword-uri-fixup");
-
-      MenuTouchModeObserver.uninit();
-      BrowserOffline.uninit();
-      CanvasPermissionPromptHelper.uninit();
-      WebAuthnPromptHelper.uninit();
-      PanelUI.uninit();
-    }
-
-    // Final window teardown, do this last.
-    gBrowser.destroy();
-    window.XULBrowserWindow = null;
-    window.docShell.treeOwner
-      .QueryInterface(Ci.nsIInterfaceRequestor)
-      .getInterface(Ci.nsIAppWindow).XULBrowserWindow = null;
-    window.browserDOMWindow = null;
-  },
-};
-
-ChromeUtils.defineLazyGetter(
-  gBrowserInit,
-  "_firstContentWindowPaintDeferred",
-  () => Promise.withResolvers()
-);
-
-gBrowserInit.idleTasksFinishedPromise = new Promise(resolve => {
-  gBrowserInit.idleTaskPromiseResolve = resolve;
-});
-
 function HandleAppCommandEvent(evt) {
   switch (evt.command) {
     case "Back":
@@ -2634,7 +1524,7 @@ function HandleAppCommandEvent(evt) {
       BrowserSearch.webSearch();
       break;
     case "Bookmarks":
-      SidebarUI.toggle("viewBookmarksSidebar");
+      SidebarController.toggle("viewBookmarksSidebar");
       break;
     case "Home":
       BrowserCommands.home();
@@ -3636,7 +2526,7 @@ const BrowserSearch = {
     event
   ) {
     event = getRootEvent(event);
-    let where = whereToOpenLink(event);
+    let where = BrowserUtils.whereToOpenLink(event);
     if (where == "current") {
       // override: historically search opens in new tab
       where = "tab";
@@ -3942,14 +2832,6 @@ function FillHistoryMenu(aParent) {
   return true;
 }
 
-function BrowserDownloadsUI() {
-  if (PrivateBrowsingUtils.isWindowPrivate(window)) {
-    openTrustedLinkIn("about:downloads", "tab");
-  } else {
-    PlacesCommandHook.showPlacesOrganizer("Downloads");
-  }
-}
-
 function toOpenWindowByType(inType, uri, features) {
   var topWindow = Services.wm.getMostRecentWindow(inType);
 
@@ -4850,7 +3732,7 @@ var XULBrowserWindow = {
       }
     }
 
-    if (TranslationsParent.isRestrictedPage(gBrowser)) {
+    if (TranslationsParent.isFullPageTranslationsRestrictedForPage(gBrowser)) {
       this._menuItemForTranslations.setAttribute("disabled", "true");
     } else {
       this._menuItemForTranslations.removeAttribute("disabled");
@@ -5658,7 +4540,7 @@ nsBrowserAccess.prototype = {
       : PrivateBrowsingUtils.isWindowPrivate(window);
 
     switch (aWhere) {
-      case Ci.nsIBrowserDOMWindow.OPEN_NEWWINDOW:
+      case Ci.nsIBrowserDOMWindow.OPEN_NEWWINDOW: {
         // FIXME: Bug 408379. So how come this doesn't send the
         // referrer like the other loads do?
         var url = aURI && aURI.spec;
@@ -5702,6 +4584,7 @@ nsBrowserAccess.prototype = {
           console.error(ex);
         }
         break;
+      }
       case Ci.nsIBrowserDOMWindow.OPEN_NEWTAB:
       case Ci.nsIBrowserDOMWindow.OPEN_NEWTAB_BACKGROUND: {
         // If we have an opener, that means that the caller is expecting access
@@ -6112,7 +4995,7 @@ function setToolbarVisibility(
         document.documentElement.toggleAttribute(overlapAttr, false);
         break;
       case "newtab":
-      default:
+      default: {
         let currentURI = gBrowser?.currentURI;
         if (!gBrowserInit.domContentLoaded) {
           let uriToLoad = gBrowserInit.uriToLoadPromise;
@@ -6129,6 +5012,7 @@ function setToolbarVisibility(
         isVisible = BookmarkingUI.isOnNewTabPage(currentURI);
         document.documentElement.toggleAttribute(overlapAttr, isVisible);
         break;
+      }
     }
   }
 
@@ -6285,9 +5169,10 @@ var gUIDensity = {
     }
 
     let docs = [document.documentElement];
-    let shouldUpdateSidebar = SidebarUI.initialized && SidebarUI.isOpen;
+    let shouldUpdateSidebar =
+      SidebarController.initialized && SidebarController.isOpen;
     if (shouldUpdateSidebar) {
-      docs.push(SidebarUI.browser.contentDocument.documentElement);
+      docs.push(SidebarController.browser.contentDocument.documentElement);
     }
     for (let doc of docs) {
       switch (mode) {
@@ -6303,7 +5188,7 @@ var gUIDensity = {
       }
     }
     if (shouldUpdateSidebar) {
-      let tree = SidebarUI.browser.contentDocument.querySelector(
+      let tree = SidebarController.browser.contentDocument.querySelector(
         ".sidebar-placesTree"
       );
       if (tree) {
@@ -6540,7 +5425,7 @@ function handleLinkClick(event, href, linkNode) {
     return false;
   }
 
-  var where = whereToOpenLink(event);
+  var where = BrowserUtils.whereToOpenLink(event);
   if (where == "current") {
     return false;
   }
@@ -6613,7 +5498,7 @@ function middleMousePaste(event) {
 
   // if it's not the current tab, we don't need to do anything because the
   // browser doesn't exist.
-  let where = whereToOpenLink(event, true, false);
+  let where = BrowserUtils.whereToOpenLink(event, true, false);
   let lastLocationChange;
   if (where == "current") {
     lastLocationChange = gBrowser.selectedBrowser.lastLocationChange;
@@ -6727,13 +5612,6 @@ function handleDroppedLink(
   }
 }
 
-function BrowserForceEncodingDetection() {
-  gBrowser.selectedBrowser.forceEncodingDetection();
-  BrowserCommands.reloadWithFlags(
-    Ci.nsIWebNavigation.LOAD_FLAGS_CHARSET_CHANGE
-  );
-}
-
 var ToolbarContextMenu = {
   updateDownloadsAutoHide(popup) {
     let checkbox = document.getElementById(
@@ -7628,84 +6506,6 @@ var MailIntegration = {
   },
 };
 
-/**
- * Open about:addons page by given view id.
- * @param {String} aView
- *                 View id of page that will open.
- *                 e.g. "addons://discover/"
- * @param {Object} options
- *        {
- *          selectTabByViewId: If true, if there is the tab opening page having
- *                             same view id, select the tab. Else if the current
- *                             page is blank, load on it. Otherwise, open a new
- *                             tab, then load on it.
- *                             If false, if there is the tab opening
- *                             about:addoons page, select the tab and load page
- *                             for view id on it. Otherwise, leave the loading
- *                             behavior to switchToTabHavingURI().
- *                             If no options, handles as false.
- *        }
- * @returns {Promise} When the Promise resolves, returns window object loaded the
- *                    view id.
- */
-function BrowserOpenAddonsMgr(aView, { selectTabByViewId = false } = {}) {
-  return new Promise(resolve => {
-    let emWindow;
-    let browserWindow;
-
-    var receivePong = function (aSubject) {
-      let browserWin = aSubject.browsingContext.topChromeWindow;
-      if (!emWindow || browserWin == window /* favor the current window */) {
-        if (
-          selectTabByViewId &&
-          aSubject.gViewController.currentViewId !== aView
-        ) {
-          return;
-        }
-
-        emWindow = aSubject;
-        browserWindow = browserWin;
-      }
-    };
-    Services.obs.addObserver(receivePong, "EM-pong");
-    Services.obs.notifyObservers(null, "EM-ping");
-    Services.obs.removeObserver(receivePong, "EM-pong");
-
-    if (emWindow) {
-      if (aView && !selectTabByViewId) {
-        emWindow.loadView(aView);
-      }
-      let tab = browserWindow.gBrowser.getTabForBrowser(
-        emWindow.docShell.chromeEventHandler
-      );
-      browserWindow.gBrowser.selectedTab = tab;
-      emWindow.focus();
-      resolve(emWindow);
-      return;
-    }
-
-    if (selectTabByViewId) {
-      const target = isBlankPageURL(gBrowser.currentURI.spec)
-        ? "current"
-        : "tab";
-      openTrustedLinkIn("about:addons", target);
-    } else {
-      // This must be a new load, else the ping/pong would have
-      // found the window above.
-      switchToTabHavingURI("about:addons", true);
-    }
-
-    Services.obs.addObserver(function observer(aSubject, aTopic) {
-      Services.obs.removeObserver(observer, aTopic);
-      if (aView) {
-        aSubject.loadView(aView);
-      }
-      aSubject.focus();
-      resolve(aSubject);
-    }, "EM-loaded");
-  });
-}
-
 function AddKeywordForSearchField() {
   if (!gContextMenu) {
     throw new Error("Context menu doesn't seem to be open.");
@@ -8256,7 +7056,7 @@ function safeModeRestart() {
  */
 function duplicateTabIn(aTab, where, delta) {
   switch (where) {
-    case "window":
+    case "window": {
       let otherWin = OpenBrowserWindow({
         private: PrivateBrowsingUtils.isBrowserPrivate(aTab.linkedBrowser),
       });
@@ -8278,6 +7078,7 @@ function duplicateTabIn(aTab, where, delta) {
         "browser-delayed-startup-finished"
       );
       break;
+    }
     case "tabshifted":
       SessionStore.duplicateTab(window, aTab, delta);
       // A background tab has been opened, nothing else to do here.
@@ -9125,15 +7926,14 @@ var ConfirmationHint = {
    *         - event (DOM event): The event that triggered the feedback
    *         - descriptionId (string): message ID of the description text
    *         - position (string): position of the panel relative to the anchor.
-   *
+   *         - l10nArgs (object): l10n arguments for the messageId.
    */
   show(anchor, messageId, options = {}) {
     this._reset();
 
     MozXULElement.insertFTLIfNeeded("toolkit/branding/brandings.ftl");
     MozXULElement.insertFTLIfNeeded("browser/confirmationHints.ftl");
-    document.l10n.setAttributes(this._message, messageId);
-
+    document.l10n.setAttributes(this._message, messageId, options.l10nArgs);
     if (options.descriptionId) {
       document.l10n.setAttributes(this._description, options.descriptionId);
       this._description.hidden = false;
@@ -9236,11 +8036,9 @@ var FirefoxViewHandler = {
     ChromeUtils.defineESModuleGetters(this, {
       SyncedTabs: "resource://services-sync/SyncedTabs.sys.mjs",
     });
-    Services.obs.addObserver(this, "firefoxview-notification-dot-update");
   },
   uninit() {
     CustomizableUI.removeListener(this);
-    Services.obs.removeObserver(this, "firefoxview-notification-dot-update");
   },
   onWidgetRemoved(aWidgetId) {
     if (aWidgetId == this.BUTTON_ID && this.tab) {
@@ -9293,7 +8091,7 @@ var FirefoxViewHandler = {
   },
   handleEvent(e) {
     switch (e.type) {
-      case "TabSelect":
+      case "TabSelect": {
         const selected = e.target == this.tab;
         this.button?.toggleAttribute("open", selected);
         this.button?.setAttribute("aria-pressed", selected);
@@ -9304,6 +8102,7 @@ var FirefoxViewHandler = {
         gBrowser.visibleTabs[0].style.MozUserFocus =
           e.target == this.tab ? "normal" : "";
         break;
+      }
       case "TabClose":
         this.tab = null;
         gBrowser.tabContainer.removeEventListener("TabSelect", this);
@@ -9314,14 +8113,6 @@ var FirefoxViewHandler = {
         break;
     }
   },
-  observe(sub, topic, data) {
-    switch (topic) {
-      case "firefoxview-notification-dot-update":
-        let shouldShow = data === "true";
-        this._toggleNotificationDot(shouldShow);
-        break;
-    }
-  },
   _closeDeviceConnectedTab() {
     if (!TabsSetupFlowManager.didFxaTabOpen) {
       return;
@@ -9352,11 +8143,6 @@ var FirefoxViewHandler = {
   _onTabForegrounded() {
     if (this.tab?.selected) {
       this.SyncedTabs.syncTabs();
-      Services.obs.notifyObservers(
-        null,
-        "firefoxview-notification-dot-update",
-        "false"
-      );
     }
   },
   _recordViewIfTabSelected() {
@@ -9380,7 +8166,4 @@ var FirefoxViewHandler = {
       }
     }
   },
-  _toggleNotificationDot(shouldShow) {
-    this.button?.toggleAttribute("attention", shouldShow);
-  },
 };
diff --git a/browser/base/content/browser.js.globals b/browser/base/content/browser.js.globals
index 7002cd0b5b..910e0b5ca9 100644
--- a/browser/base/content/browser.js.globals
+++ b/browser/base/content/browser.js.globals
@@ -28,9 +28,6 @@
   "gPopupBlockerObserver",
   "gKeywordURIFixup",
   "_createNullPrincipalFromTabUserContextId",
-  "_resolveDelayedStartup",
-  "delayedStartupPromise",
-  "gBrowserInit",
   "HandleAppCommandEvent",
   "BrowserCommands",
   "kSkipCacheFlags",
@@ -54,7 +51,6 @@
   "BrowserSearch",
   "CreateContainerTabMenu",
   "FillHistoryMenu",
-  "BrowserDownloadsUI",
   "toOpenWindowByType",
   "OpenBrowserWindow",
   "updateEditUIVisibility",
@@ -85,7 +81,6 @@
   "handleLinkClick",
   "middleMousePaste",
   "handleDroppedLink",
-  "BrowserForceEncodingDetection",
   "ToolbarContextMenu",
   "BrowserOffline",
   "CanvasPermissionPromptHelper",
@@ -94,7 +89,6 @@
   "WindowIsClosing",
   "warnAboutClosingWindow",
   "MailIntegration",
-  "BrowserOpenAddonsMgr",
   "AddKeywordForSearchField",
   "restoreLastClosedTabOrWindowOrSession",
   "undoCloseTab",
@@ -135,7 +129,6 @@
   "DownloadsCommon",
   "E10SUtils",
   "ExtensionsUI",
-  "FirefoxViewNotificationManager",
   "HomePage",
   "isProductURL",
   "LightweightThemeConsumer",
diff --git a/browser/base/content/browser.xhtml b/browser/base/content/browser.xhtml
index 8ef14813b1..aec0983a67 100644
--- a/browser/base/content/browser.xhtml
+++ b/browser/base/content/browser.xhtml
@@ -39,7 +39,6 @@
   <link rel="stylesheet" href="chrome://global/skin/global.css" />
 
   <link rel="stylesheet" href="chrome://browser/content/browser.css" />
-  <link rel="stylesheet" href="chrome://browser/content/tabbrowser.css" />
   <link
     rel="stylesheet"
     href="chrome://browser/content/downloads/downloads.css"
@@ -84,7 +83,6 @@
   <link rel="localization" href="browser/translations.ftl" />
   <link rel="localization" href="browser/unifiedExtensions.ftl"/>
   <link rel="localization" href="browser/webrtcIndicator.ftl"/>
-  <link rel="localization" href="toolkit/branding/accounts.ftl"/>
   <link rel="localization" href="toolkit/branding/brandings.ftl"/>
   <link rel="localization" href="toolkit/global/contextual-identity.ftl"/>
   <link rel="localization" href="toolkit/global/textActions.ftl"/>
@@ -107,6 +105,7 @@
 
 <script>
   /* eslint-env mozilla/browser-window */
+  Services.scriptloader.loadSubScript("chrome://browser/content/browser-init.js", this);
   Services.scriptloader.loadSubScript("chrome://global/content/contentAreaUtils.js", this);
   Services.scriptloader.loadSubScript("chrome://browser/content/browser-captivePortal.js", this);
   if (AppConstants.MOZ_DATA_REPORTING) {
diff --git a/browser/base/content/macWindow.inc.xhtml b/browser/base/content/macWindow.inc.xhtml
index b9ca44c7eb..b5afa5f644 100644
--- a/browser/base/content/macWindow.inc.xhtml
+++ b/browser/base/content/macWindow.inc.xhtml
@@ -16,7 +16,6 @@
   <html:link rel="localization" href="browser/menubar.ftl"/>
   <html:link rel="localization" href="browser/reportBrokenSite.ftl"/>
   <html:link rel="localization" href="browser/screenshots.ftl"/>
-  <html:link rel="localization" href="toolkit/branding/accounts.ftl"/>
   <html:link rel="localization" href="toolkit/branding/brandings.ftl"/>
   <html:link rel="localization" href="toolkit/global/textActions.ftl"/>
 </linkset>
diff --git a/browser/base/content/main-popupset.inc.xhtml b/browser/base/content/main-popupset.inc.xhtml
index 91b2483c53..ef8245938e 100644
--- a/browser/base/content/main-popupset.inc.xhtml
+++ b/browser/base/content/main-popupset.inc.xhtml
@@ -77,13 +77,16 @@
               data-lazy-l10n-id="tab-context-close-n-tabs"
               data-l10n-args='{"tabCount": 1}'
               oncommand="TabContextMenu.closeContextTabs();"/>
+    <menuitem id="context_closeDuplicateTabs"
+              data-lazy-l10n-id="tab-context-close-duplicate-tabs"
+              oncommand="gBrowser.removeDuplicateTabs(TabContextMenu.contextTab);"/>
     <menu id="context_closeTabOptions"
           data-lazy-l10n-id="tab-context-close-multiple-tabs">
       <menupopup id="closeTabOptions">
         <menuitem id="context_closeTabsToTheStart" data-lazy-l10n-id="close-tabs-to-the-start"
-                  oncommand="gBrowser.removeTabsToTheStartFrom(TabContextMenu.contextTab, {animate: true});"/>
+                  oncommand="gBrowser.removeTabsToTheStartFrom(TabContextMenu.contextTab);"/>
         <menuitem id="context_closeTabsToTheEnd" data-lazy-l10n-id="close-tabs-to-the-end"
-                  oncommand="gBrowser.removeTabsToTheEndFrom(TabContextMenu.contextTab, {animate: true});"/>
+                  oncommand="gBrowser.removeTabsToTheEndFrom(TabContextMenu.contextTab);"/>
         <menuitem id="context_closeOtherTabs" data-lazy-l10n-id="close-other-tabs"
                   oncommand="gBrowser.removeAllTabsBut(TabContextMenu.contextTab);"/>
       </menupopup>
@@ -253,26 +256,26 @@
     <menuitem id="sidebar-switcher-bookmarks"
               data-l10n-id="sidebar-menu-bookmarks"
               key="viewBookmarksSidebarKb"
-              oncommand="SidebarUI.show('viewBookmarksSidebar');"/>
+              oncommand="SidebarController.show('viewBookmarksSidebar');"/>
     <menuitem id="sidebar-switcher-history"
               data-l10n-id="sidebar-menu-history"
               key="key_gotoHistory"
-              oncommand="SidebarUI.show('viewHistorySidebar');"/>
+              oncommand="SidebarController.show('viewHistorySidebar');"/>
     <menuitem id="sidebar-switcher-tabs"
               data-l10n-id="sidebar-menu-synced-tabs"
               class="sync-ui-item"
-              oncommand="SidebarUI.show('viewTabsSidebar');"/>
+              oncommand="SidebarController.show('viewTabsSidebar');"/>
     <menuitem id="sidebar-switcher-megalist"
               data-l10n-id="sidebar-menu-megalist"
-              oncommand="SidebarUI.show('viewMegalistSidebar');"/>
+              oncommand="SidebarController.show('viewMegalistSidebar');"/>
     <menuseparator/>
     <!-- Extension toolbarbuttons go here. -->
     <menuseparator id="sidebar-extensions-separator"/>
     <menuitem id="sidebar-reverse-position"
-              oncommand="SidebarUI.reversePosition()"/>
+              oncommand="SidebarController.reversePosition()"/>
     <menuseparator/>
     <menuitem data-l10n-id="sidebar-menu-close"
-              oncommand="SidebarUI.hide()"/>
+              oncommand="SidebarController.hide()"/>
   </menupopup>
 
   <menupopup id="toolbar-context-menu"
@@ -426,6 +429,10 @@
     <html:div class="tab-preview-text-container">
       <html:div class="tab-preview-title"></html:div>
       <html:div class="tab-preview-uri"></html:div>
+      <html:div class="tab-preview-pid-activeness">
+        <html:div class="tab-preview-pid"></html:div>
+        <html:div class="tab-preview-activeness"></html:div>
+      </html:div>
     </html:div>
     <html:div class="tab-preview-thumbnail-container"></html:div>
   </panel>
@@ -675,4 +682,14 @@
     <menuitem data-l10n-id="translations-panel-settings-about2"
               oncommand="FullPageTranslationsPanel.onAboutTranslations()"/>
   </menupopup>
+
+  <menupopup id="select-translations-panel-settings-menupopup">
+    <menuitem id="select-translations-panel-open-settings-page-menuitem"
+              class="manage-languages-menuitem"
+              data-l10n-id="select-translations-panel-open-translations-settings-menuitem"
+              oncommand="SelectTranslationsPanel.openTranslationsSettingsPage()"/>
+    <menuitem id="select-translations-panel-about-translations-menuitem"
+              data-l10n-id="translations-panel-settings-about2"
+              oncommand="SelectTranslationsPanel.onAboutTranslations()"/>
+  </menupopup>
 </popupset>
diff --git a/browser/base/content/navigator-toolbox.inc.xhtml b/browser/base/content/navigator-toolbox.inc.xhtml
index a86d01adb2..0a67afa81f 100644
--- a/browser/base/content/navigator-toolbox.inc.xhtml
+++ b/browser/base/content/navigator-toolbox.inc.xhtml
@@ -100,6 +100,9 @@
         <image class="private-browsing-indicator-icon"/>
         <label data-l10n-id="private-browsing-indicator-label"></label>
       </hbox>
+      <toolbarbutton id="content-analysis-indicator"
+                     oncommand="ContentAnalysis.showPanel(this, PanelUI);"
+                     class="toolbarbutton-1 content-analysis-indicator-icon"/>
 
 #include titlebar-items.inc.xhtml
 
@@ -509,12 +512,12 @@
            customizable="true">
     <toolbartabstop skipintoolbarset="true"/>
 
-    <hbox id="personal-toolbar-empty" skipintoolbarset="true" removable="false" hidden="true">
+    <hbox id="personal-toolbar-empty" skipintoolbarset="true" removable="false" hidden="true" role="alert">
       <description id="personal-toolbar-empty-description"
                    data-l10n-id="bookmarks-toolbar-empty-message"
                    onclick="BookmarkingUI.openLibraryIfLinkClicked(event);"
                    onkeydown="BookmarkingUI.openLibraryIfLinkClicked(event);">
-        <html:a data-l10n-name="manage-bookmarks" class="text-link" tabindex="0"/>
+        <html:a data-l10n-name="manage-bookmarks" class="text-link" tabindex="0" role="link"/>
       </description>
     </hbox>
 
@@ -618,7 +621,7 @@
         <menuitem id="BMB_viewBookmarksSidebar"
                   data-l10n-id="bookmarks-tools-sidebar-visibility"
                   data-l10n-args='{ "isVisible": false }'
-                  oncommand="SidebarUI.toggle('viewBookmarksSidebar');"
+                  oncommand="SidebarController.toggle('viewBookmarksSidebar');"
                   key="viewBookmarksSidebarKb"/>
         <menuitem id="BMB_searchBookmarks"
                   data-l10n-id="bookmarks-search"
diff --git a/browser/base/content/nsContextMenu.js b/browser/base/content/nsContextMenu.js
index 9769552dce..1811dfcaca 100644
--- a/browser/base/content/nsContextMenu.js
+++ b/browser/base/content/nsContextMenu.js
@@ -1347,8 +1347,6 @@ class nsContextMenu {
       !this.onTextInput &&
       !this.onLink &&
       !this.onPlainTextLink &&
-      !this.onImage &&
-      !this.onVideo &&
       !this.onAudio &&
       !this.onEditable &&
       !this.onPassword;
@@ -1685,7 +1683,7 @@ class nsContextMenu {
 
   // Change current window to the URL of the image, video, or audio.
   viewMedia(e) {
-    let where = whereToOpenLink(e, false, false);
+    let where = BrowserUtils.whereToOpenLink(e, false, false);
     if (where == "current") {
       where = "tab";
     }
@@ -2175,7 +2173,10 @@ class nsContextMenu {
     var clipboard = Cc["@mozilla.org/widget/clipboardhelper;1"].getService(
       Ci.nsIClipboardHelper
     );
-    clipboard.copyString(addresses);
+    clipboard.copyString(
+      addresses,
+      this.actor.manager.browsingContext.currentWindowGlobal
+    );
   }
 
   // Extract phone and put it on clipboard
@@ -2195,7 +2196,10 @@ class nsContextMenu {
     var clipboard = Cc["@mozilla.org/widget/clipboardhelper;1"].getService(
       Ci.nsIClipboardHelper
     );
-    clipboard.copyString(phone);
+    clipboard.copyString(
+      phone,
+      this.actor.manager.browsingContext.currentWindowGlobal
+    );
   }
 
   copyLink() {
@@ -2204,7 +2208,10 @@ class nsContextMenu {
     var clipboard = Cc["@mozilla.org/widget/clipboardhelper;1"].getService(
       Ci.nsIClipboardHelper
     );
-    clipboard.copyString(linkURL);
+    clipboard.copyString(
+      linkURL,
+      this.actor.manager.browsingContext.currentWindowGlobal
+    );
   }
 
   /**
@@ -2220,7 +2227,10 @@ class nsContextMenu {
       let clipboard = Cc["@mozilla.org/widget/clipboardhelper;1"].getService(
         Ci.nsIClipboardHelper
       );
-      clipboard.copyString(strippedLinkURL);
+      clipboard.copyString(
+        strippedLinkURL,
+        this.actor.manager.browsingContext.currentWindowGlobal
+      );
     }
   }
 
@@ -2324,8 +2334,8 @@ class nsContextMenu {
     try {
       strippedLinkURI = QueryStringStripper.stripForCopyOrShare(this.linkURI);
     } catch (e) {
-      console.warn(`isLinkURIStrippable: ${e.message}`);
-      return null;
+      console.warn(`stripForCopyOrShare: ${e.message}`);
+      return this.linkURI;
     }
 
     // If nothing can be stripped, we return the original URI
@@ -2458,7 +2468,10 @@ class nsContextMenu {
     var clipboard = Cc["@mozilla.org/widget/clipboardhelper;1"].getService(
       Ci.nsIClipboardHelper
     );
-    clipboard.copyString(this.originalMediaURL);
+    clipboard.copyString(
+      this.originalMediaURL,
+      this.actor.manager.browsingContext.currentWindowGlobal
+    );
   }
 
   getImageText() {
@@ -2484,7 +2497,7 @@ class nsContextMenu {
     let drmInfoURL =
       Services.urlFormatter.formatURLPref("app.support.baseURL") +
       "drm-content";
-    let dest = whereToOpenLink(aEvent);
+    let dest = BrowserUtils.whereToOpenLink(aEvent);
     // Don't ever want this to open in the same tab as it'll unload the
     // DRM'd video, which is going to be a bad idea in most cases.
     if (dest == "current") {
@@ -2526,7 +2539,7 @@ class nsContextMenu {
       screenY,
       this.#getTextToTranslate(),
       this.#translationsLangPairPromise
-    );
+    ).catch(console.error);
   }
 
   /**
@@ -2606,6 +2619,8 @@ class nsContextMenu {
     translateSelectionItem.hidden =
       // Only show the item if the feature is enabled.
       !(translationsEnabled && selectTranslationsEnabled) ||
+      // Only show the item if Translations is supported on this hardware.
+      !TranslationsParent.getIsTranslationsEngineSupported() ||
       // If there is no text to translate, we have nothing to do.
       textToTranslate.length === 0 ||
       // We do not allow translating selections on top of Full Page Translations.
diff --git a/browser/base/content/popup-notifications.inc b/browser/base/content/popup-notifications.inc
index daee34e6fe..3d57f4808c 100644
--- a/browser/base/content/popup-notifications.inc
+++ b/browser/base/content/popup-notifications.inc
@@ -35,7 +35,7 @@
         <description id="webRTC-all-windows-shared" hidden="true" data-l10n-id="popup-all-windows-shared"></description>
       </popupnotificationcontent>
 
-      <popupnotificationcontent id="webRTC-preview" hidden="true">
+      <popupnotificationcontent id="webRTC-preview" orient="vertical" hidden="true">
         <html:video id="webRTC-previewVideo" tabindex="-1"/>
         <vbox id="webRTC-previewWarningBox">
           <description id="webRTC-previewWarning"/>
diff --git a/browser/base/content/spotlight.html b/browser/base/content/spotlight.html
index a948f8dbf4..216f290efd 100644
--- a/browser/base/content/spotlight.html
+++ b/browser/base/content/spotlight.html
@@ -19,6 +19,7 @@
     <link rel="localization" href="branding/brand.ftl" />
     <link rel="localization" href="toolkit/branding/brandings.ftl" />
     <link rel="localization" href="browser/newtab/asrouter.ftl" />
+    <link rel="localization" href="preview/onboarding.ftl" />
     <link rel="localization" href="browser/newtab/onboarding.ftl" />
     <link rel="localization" href="browser/spotlight.ftl" />
     <link rel="localization" href="browser/migrationWizard.ftl" />
diff --git a/browser/base/content/tabbrowser-tabs.js b/browser/base/content/tabbrowser-tabs.js
index 7784e74ed3..9b30584077 100644
--- a/browser/base/content/tabbrowser-tabs.js
+++ b/browser/base/content/tabbrowser-tabs.js
@@ -125,23 +125,14 @@
         this.tabbox.tabpanels.setAttribute("async", "true");
       }
 
-      this.configureTooltip = () => {
-        // fall back to original tooltip behavior if pref is not set
-        if (this._showCardPreviews) {
-          this.tooltip = null;
-        } else {
-          this.tooltip = "tabbrowser-tab-tooltip";
-          this._previewPanel = null;
-        }
-      };
       XPCOMUtils.defineLazyPreferenceGetter(
         this,
         "_showCardPreviews",
         TAB_PREVIEW_PREF,
-        false,
-        () => this.configureTooltip()
+        false
       );
-      this.configureTooltip();
+      this.tooltip = "tabbrowser-tab-tooltip";
+      this._previewPanel = null;
     }
 
     on_TabSelect() {
diff --git a/browser/base/content/tabbrowser.css b/browser/base/content/tabbrowser.css
deleted file mode 100644
index 120203141c..0000000000
--- a/browser/base/content/tabbrowser.css
+++ /dev/null
@@ -1,101 +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/. */
-
-.tab-close-button[pinned],
-#tabbrowser-tabs[closebuttons="activetab"] > #tabbrowser-arrowscrollbox > .tabbrowser-tab > .tab-stack > .tab-content > .tab-close-button:not([selected]),
-.tab-icon-pending:not([pendingicon]),
-.tab-icon-pending[busy],
-.tab-icon-pending[pinned],
-.tab-icon-image:not([src], [pinned], [crashed], [pictureinpicture])[selected],
-.tab-icon-image:not([src], [pinned], [crashed], [sharing], [pictureinpicture]),
-.tab-icon-image[busy],
-.tab-throbber:not([busy]),
-.tab-sharing-icon-overlay,
-.tab-icon-overlay {
-  display: none;
-}
-
-:root[uidensity=compact] .tab-secondary-label,
-.tab-secondary-label:not([soundplaying], [muted], [activemedia-blocked], [pictureinpicture]),
-.tab-secondary-label:not([activemedia-blocked]) > .tab-icon-sound-blocked-label,
-.tab-secondary-label[muted][activemedia-blocked] > .tab-icon-sound-blocked-label,
-.tab-secondary-label[activemedia-blocked] > .tab-icon-sound-playing-label,
-.tab-secondary-label[muted] > .tab-icon-sound-playing-label,
-.tab-secondary-label[pictureinpicture] > .tab-icon-sound-playing-label,
-.tab-secondary-label[pictureinpicture] > .tab-icon-sound-muted-label,
-.tab-secondary-label:not([pictureinpicture]) > .tab-icon-sound-pip-label,
-.tab-secondary-label:not([muted]) > .tab-icon-sound-muted-label,
-.tab-secondary-label:not([showtooltip]) > .tab-icon-sound-tooltip-label,
-.tab-secondary-label[showtooltip] > .tab-icon-sound-label:not(.tab-icon-sound-tooltip-label) {
-  display: none;
-}
-
-.tab-sharing-icon-overlay[sharing]:not([selected]),
-.tab-icon-overlay:is([soundplaying], [muted], [activemedia-blocked], [crashed]) {
-  display: revert;
-}
-
-.tabbrowser-tab {
-  --tab-label-mask-size: 2em;
-}
-
-.tab-label {
-  white-space: nowrap;
-  line-height: 1.7;  /* override 'normal' in case of fallback math fonts with huge metrics */
-}
-
-.tab-secondary-label {
-  margin: -.3em 0 .3em; /* adjust margins to compensate for line-height of .tab-label */
-}
-
-.tab-label-container {
-  overflow: hidden;
-}
-
-.tab-label-container[pinned] {
-  width: 0;
-}
-
-.tab-label-container[textoverflow][labeldirection=ltr]:not([pinned]),
-.tab-label-container[textoverflow]:not([labeldirection], [pinned]):-moz-locale-dir(ltr) {
-  direction: ltr;
-  mask-image: linear-gradient(to left, transparent, black var(--tab-label-mask-size));
-}
-
-.tab-label-container[textoverflow][labeldirection=rtl]:not([pinned]),
-.tab-label-container[textoverflow]:not([labeldirection], [pinned]):-moz-locale-dir(rtl) {
-  direction: rtl;
-  mask-image: linear-gradient(to right, transparent, black var(--tab-label-mask-size));
-}
-
-tabpanels {
-  background-color: transparent;
-}
-
-/* Apply crisp rendering for favicons at exactly 2dppx resolution */
-@media (resolution: 2dppx) {
-  .tab-icon-image {
-    image-rendering: -moz-crisp-edges;
-  }
-}
-
-.closing-tabs-spacer {
-  pointer-events: none;
-}
-
-#tabbrowser-arrowscrollbox:not(:hover) > #tabbrowser-arrowscrollbox-periphery > .closing-tabs-spacer {
-  transition: width .15s ease-out;
-}
-
-browser[blank],
-browser[pendingpaint] {
-  opacity: 0;
-}
-
-#tabbrowser-tabpanels[pendingpaint] {
-  background-image: url(chrome://browser/skin/tabbrowser/pendingpaint.png);
-  background-repeat: no-repeat;
-  background-position: center center;
-  background-size: 30px;
-}
diff --git a/browser/base/content/tabbrowser.js b/browser/base/content/tabbrowser.js
index 3bca0b6d30..f319fd5d46 100644
--- a/browser/base/content/tabbrowser.js
+++ b/browser/base/content/tabbrowser.js
@@ -67,7 +67,7 @@
     replaceContainerClass("color", hbox, identity.color);
 
     let label = ContextualIdentityService.getUserContextLabel(userContextId);
-    document.getElementById("userContext-label").setAttribute("value", label);
+    document.getElementById("userContext-label").textContent = label;
     // Also set the container label as the tooltip so we can only show the icon
     // in small windows.
     hbox.setAttribute("tooltiptext", label);
@@ -110,6 +110,12 @@
         "privacy.exposeContentTitleInWindow.pbm",
         true
       );
+      XPCOMUtils.defineLazyPreferenceGetter(
+        this,
+        "_showTabCardPreview",
+        "browser.tabs.cardPreview.enabled",
+        true
+      );
 
       if (AppConstants.MOZ_CRASHREPORTER) {
         ChromeUtils.defineESModuleGetters(this, {
@@ -161,6 +167,8 @@
       TO_START: 2,
       TO_END: 3,
       MULTI_SELECTED: 4,
+      DUPLICATES: 6,
+      ALL_DUPLICATES: 7,
     },
 
     _lastRelatedTabMap: new WeakMap(),
@@ -348,6 +356,90 @@
       return this.tabContainer._getVisibleTabs();
     },
 
+    getDuplicateTabsToClose(aTab) {
+      // One would think that a set is better, but it would need to copy all
+      // the strings instead of just keeping references to the nsIURI objects,
+      // and the array is presumed to be small anyways.
+      let keys = [];
+      let keyForTab = tab => {
+        let uri = tab.linkedBrowser?.currentURI;
+        if (!uri) {
+          return null;
+        }
+        return {
+          uri,
+          userContextId: tab.userContextId,
+        };
+      };
+      let keyEquals = (a, b) => {
+        return a.userContextId == b.userContextId && a.uri.equals(b.uri);
+      };
+      if (aTab.multiselected) {
+        for (let tab of this.selectedTabs) {
+          let key = keyForTab(tab);
+          if (key) {
+            keys.push(key);
+          }
+        }
+      } else {
+        let key = keyForTab(aTab);
+        if (key) {
+          keys.push(key);
+        }
+      }
+
+      if (!keys.length) {
+        return [];
+      }
+
+      let duplicateTabs = [];
+      for (let tab of this.tabs) {
+        if (tab == aTab || tab.pinned) {
+          continue;
+        }
+        if (aTab.multiselected && tab.multiselected) {
+          continue;
+        }
+        let key = keyForTab(tab);
+        if (key && keys.some(k => keyEquals(k, key))) {
+          duplicateTabs.push(tab);
+        }
+      }
+
+      return duplicateTabs;
+    },
+
+    getAllDuplicateTabsToClose() {
+      let lastSeenTabs = this.tabs.toSorted(
+        (a, b) => b.lastSeenActive - a.lastSeenActive
+      );
+      let duplicateTabs = [];
+      let keys = [];
+      for (let tab of lastSeenTabs) {
+        const uri = tab.linkedBrowser?.currentURI;
+        if (!uri) {
+          // Can't tell if it's a duplicate without a URI.
+          // Safest to leave it be.
+          continue;
+        }
+
+        const key = {
+          uri,
+          userContextId: tab.userContextId,
+        };
+        if (
+          !tab.pinned &&
+          keys.some(
+            k => k.userContextId == key.userContextId && k.uri.equals(key.uri)
+          )
+        ) {
+          duplicateTabs.push(tab);
+        }
+        keys.push(key);
+      }
+      return duplicateTabs;
+    },
+
     get _numPinnedTabs() {
       for (var i = 0; i < this.tabs.length; i++) {
         if (!this.tabs[i].pinned) {
@@ -1108,6 +1200,11 @@
         return;
       }
 
+      let oldBrowser = this.selectedBrowser;
+      // Once the async switcher starts, it's unpredictable when it will touch
+      // the address bar, thus we store its state immediately.
+      gURLBar?.saveSelectionStateForBrowser(oldBrowser);
+
       let newTab = this.getTabForBrowser(newBrowser);
 
       if (!aForceUpdate) {
@@ -1137,8 +1234,6 @@
       }
       this._lastRelatedTabMap = new WeakMap();
 
-      let oldBrowser = this.selectedBrowser;
-
       if (!gMultiProcessBrowser) {
         oldBrowser.removeAttribute("primary");
         oldBrowser.docShellIsActive = false;
@@ -1146,11 +1241,6 @@
         newBrowser.docShellIsActive = !document.hidden;
       }
 
-      if (gURLBar) {
-        oldBrowser._urlbarSelectionStart = gURLBar.selectionStart;
-        oldBrowser._urlbarSelectionEnd = gURLBar.selectionEnd;
-      }
-
       this._selectedBrowser = newBrowser;
       this._selectedTab = newTab;
       this.showTab(newTab);
@@ -1445,19 +1535,12 @@
                 if (currentActiveElement != document.activeElement) {
                   return;
                 }
-
-                gURLBar.setSelectionRange(
-                  newBrowser._urlbarSelectionStart,
-                  newBrowser._urlbarSelectionEnd
-                );
+                gURLBar.restoreSelectionStateForBrowser(newBrowser);
               },
               { once: true }
             );
           } else {
-            gURLBar.setSelectionRange(
-              newBrowser._urlbarSelectionStart,
-              newBrowser._urlbarSelectionEnd
-            );
+            gURLBar.restoreSelectionStateForBrowser(newBrowser);
           }
         };
 
@@ -1610,6 +1693,22 @@
 
     _dataURLRegEx: /^data:[^,]+;base64,/i,
 
+    // Regex to test if a string (potential tab label) consists of only non-
+    // printable characters. We consider Unicode categories Separator
+    // (spaces & line-breaks) and Other (control chars, private use, non-
+    // character codepoints) to be unprintable, along with a few specific
+    // characters whose expected rendering is blank:
+    //   U+2800 BRAILLE PATTERN BLANK (category So)
+    //   U+115F HANGUL CHOSEONG FILLER (category Lo)
+    //   U+1160 HANGUL JUNGSEONG FILLER (category Lo)
+    //   U+3164 HANGUL FILLER (category Lo)
+    //   U+FFA0 HALFWIDTH HANGUL FILLER (category Lo)
+    // We also ignore combining marks, as in the absence of a printable base
+    // character they are unlikely to be usefully rendered, and may well be
+    // clipped away entirely.
+    _nonPrintingRegEx:
+      /^[\p{Z}\p{C}\p{M}\u{115f}\u{1160}\u{2800}\u{3164}\u{ffa0}]*$/u,
+
     setTabTitle(aTab) {
       var browser = this.getBrowserForTab(aTab);
       var title = browser.contentTitle;
@@ -1630,6 +1729,16 @@
       }
 
       let isURL = false;
+
+      // Trim leading and trailing whitespace from the title.
+      title = title.trim();
+
+      // If the title contains only non-printing characters (or only combining
+      // marks, but no base character for them), we won't use it.
+      if (this._nonPrintingRegEx.test(title)) {
+        title = "";
+      }
+
       let isContentTitle = !!title;
       if (!title) {
         // See if we can use the URI as the title.
@@ -2118,16 +2227,12 @@
         b.setAttribute("name", name);
       }
 
-      let notificationbox = document.createXULElement("notificationbox");
-      notificationbox.setAttribute("notificationside", "top");
-
       let stack = document.createXULElement("stack");
       stack.className = "browserStack";
       stack.appendChild(b);
 
       let browserContainer = document.createXULElement("vbox");
       browserContainer.className = "browserContainer";
-      browserContainer.appendChild(notificationbox);
       browserContainer.appendChild(stack);
 
       let browserSidebarContainer = document.createXULElement("hbox");
@@ -3244,6 +3349,24 @@
         return true;
       }
 
+      const shownDupeDialogPref =
+        "browser.tabs.haveShownCloseAllDuplicateTabsWarning";
+      if (
+        aCloseTabs == this.closingTabsEnum.ALL_DUPLICATES &&
+        !Services.prefs.getBoolPref(shownDupeDialogPref, false)
+      ) {
+        // The first time a user closes all duplicate tabs, tell them what will
+        // happen and give them a chance to back away.
+        Services.prefs.setBoolPref(shownDupeDialogPref, true);
+
+        window.focus();
+        const [title, text] = this.tabLocalization.formatValuesSync([
+          { id: "tabbrowser-confirm-close-duplicate-tabs-title" },
+          { id: "tabbrowser-confirm-close-duplicate-tabs-text" },
+        ]);
+        return Services.prompt.confirm(window, title, text);
+      }
+
       const pref =
         aCloseTabs == this.closingTabsEnum.ALL
           ? "browser.tabs.warnOnClose"
@@ -3483,6 +3606,42 @@
       return tabsToEnd;
     },
 
+    removeDuplicateTabs(aTab) {
+      this._removeDuplicateTabs(
+        aTab,
+        this.getDuplicateTabsToClose(aTab),
+        this.closingTabsEnum.DUPLICATES
+      );
+    },
+
+    _removeDuplicateTabs(aConfirmationAnchor, tabs, aCloseTabs) {
+      if (!tabs.length) {
+        return;
+      }
+
+      if (!this.warnAboutClosingTabs(tabs.length, aCloseTabs)) {
+        return;
+      }
+
+      this.removeTabs(tabs);
+      ConfirmationHint.show(
+        aConfirmationAnchor,
+        "confirmation-hint-duplicate-tabs-closed",
+        { l10nArgs: { tabCount: tabs.length } }
+      );
+    },
+
+    removeAllDuplicateTabs() {
+      // I would like to have the caller provide this target,
+      // but the caller lives in a different document.
+      let alltabsButton = document.getElementById("alltabs-button");
+      this._removeDuplicateTabs(
+        alltabsButton,
+        this.getAllDuplicateTabsToClose(),
+        this.closingTabsEnum.ALL_DUPLICATES
+      );
+    },
+
     /**
      * In a multi-select context, the tabs (except pinned tabs) that are located to the
      * left of the leftmost selected tab will be removed.
@@ -4330,6 +4489,56 @@
         );
       }
     },
+    /**
+     * Closes tabs within the browser that match a given list of nsURIs. Returns
+     * any nsURIs that could not be closed successfully. This does not close any
+     * tabs that have a beforeUnload prompt
+     *
+     * @param {nsURI[]} urisToClose
+     *   The set of uris to remove.
+     * @returns {nsURI[]}
+     *  the nsURIs that weren't found in this browser
+     */
+    async closeTabsByURI(urisToClose) {
+      let remainingURIsToClose = [...urisToClose];
+      let tabsToRemove = [];
+      for (let tab of this.tabs) {
+        let currentURI = tab.linkedBrowser.currentURI;
+        // Find any URI that matches the current tab's URI
+        const matchedIndex = remainingURIsToClose.findIndex(uriToClose =>
+          uriToClose.equals(currentURI)
+        );
+
+        if (matchedIndex > -1) {
+          tabsToRemove.push(tab);
+          remainingURIsToClose.splice(matchedIndex, 1); // Remove the matched URI
+        }
+      }
+
+      if (tabsToRemove.length) {
+        const { beforeUnloadComplete, lastToClose } = this._startRemoveTabs(
+          tabsToRemove,
+          {
+            animate: false,
+            suppressWarnAboutClosingWindow: true,
+            skipPermitUnload: false,
+            skipRemoves: false,
+            skipSessionStore: false,
+          }
+        );
+
+        // Wait for the beforeUnload handlers to complete.
+        await beforeUnloadComplete;
+
+        // _startRemoveTabs doesn't close the last tab in the window
+        // for this use case, we simply close it
+        if (lastToClose) {
+          this.removeTab(lastToClose);
+        }
+      }
+      // If we still have uris, that means we couldn't find them in this window instance
+      return remainingURIsToClose;
+    },
 
     /**
      * Handles opening a new tab with mouse middleclick.
@@ -5659,6 +5868,20 @@
       }
     },
 
+    getTabPids(tab) {
+      if (!tab.linkedBrowser) {
+        return [];
+      }
+
+      // Get the PIDs of the content process and remote subframe processes
+      let [contentPid, ...framePids] = E10SUtils.getBrowserPids(
+        tab.linkedBrowser,
+        gFissionBrowser
+      );
+      let pids = contentPid ? [contentPid] : [];
+      return pids.concat(framePids.sort());
+    },
+
     getTabTooltip(tab, includeLabel = true) {
       let labelArray = [];
       if (includeLabel) {
@@ -5670,24 +5893,14 @@
           false
         )
       ) {
-        if (tab.linkedBrowser) {
-          // Show the PIDs of the content process and remote subframe processes.
-          let [contentPid, ...framePids] = E10SUtils.getBrowserPids(
-            tab.linkedBrowser,
-            gFissionBrowser
-          );
-          if (contentPid) {
-            if (framePids && framePids.length) {
-              labelArray.push(
-                `(pids ${contentPid}, ${framePids.sort().join(", ")})`
-              );
-            } else {
-              labelArray.push(`(pid ${contentPid})`);
-            }
-          }
-          if (tab.linkedBrowser.docShellIsActive) {
-            labelArray.push("[A]");
-          }
+        const pids = this.getTabPids(tab);
+        if (pids.length) {
+          let pidLabel = pids.length > 1 ? "pids" : "pid";
+          labelArray.push(`(${pidLabel} ${pids.join(", ")})`);
+        }
+
+        if (tab.linkedBrowser.docShellIsActive) {
+          labelArray.push("[A]");
         }
       }
 
@@ -5750,6 +5963,13 @@
         tooltip.label = "";
         document.l10n.setAttributes(tooltip, l10nId, l10nArgs);
       } else {
+        // Prevent the tooltip from appearing if card preview is enabled, but
+        // only if the user is not hovering over the media play icon or the
+        // close button
+        if (this._showTabCardPreview) {
+          event.preventDefault();
+          return;
+        }
         tooltip.label = this.getTabTooltip(tab, true);
       }
     },
@@ -7528,9 +7748,8 @@ var TabContextMenu = {
       tabsToMove[0] == visibleTabs[gBrowser._numPinnedTabs];
     contextMoveTabToStart.disabled = isFirstTab && allSelectedTabsAdjacent;
 
-    if (this.contextTab.hasAttribute("customizemode")) {
-      document.getElementById("context_openTabInWindow").disabled = true;
-    }
+    document.getElementById("context_openTabInWindow").disabled =
+      this.contextTab.hasAttribute("customizemode");
 
     // Only one of "Duplicate Tab"/"Duplicate Tabs" should be visible.
     document.getElementById("context_duplicateTab").hidden =
@@ -7564,6 +7783,17 @@ var TabContextMenu = {
       .getElementById("context_closeTab")
       .setAttribute("data-l10n-args", tabCountInfo);
 
+    let closeDuplicateEnabled = Services.prefs.getBoolPref(
+      "browser.tabs.context.close-duplicate.enabled"
+    );
+    let closeDuplicateTabsItem = document.getElementById(
+      "context_closeDuplicateTabs"
+    );
+    closeDuplicateTabsItem.hidden = !closeDuplicateEnabled;
+    closeDuplicateTabsItem.disabled =
+      !closeDuplicateEnabled ||
+      !gBrowser.getDuplicateTabsToClose(this.contextTab).length;
+
     // Disable "Close Multiple Tabs" if all sub menuitems are disabled
     document.getElementById("context_closeTabOptions").disabled =
       closeTabsToTheStartItem.disabled &&
diff --git a/browser/base/content/test/about/browser.toml b/browser/base/content/test/about/browser.toml
index 98961200a0..2c6dafb4dd 100644
--- a/browser/base/content/test/about/browser.toml
+++ b/browser/base/content/test/about/browser.toml
@@ -66,7 +66,6 @@ support-files = [
 ["browser_aboutNewTab_bookmarksToolbar.js"]
 
 ["browser_aboutNewTab_bookmarksToolbarEmpty.js"]
-fail-if = ["a11y_checks"] # Bug 1854233 text-link may not be focusable
 skip-if = ["tsan"] # Bug 1676326, highly frequent on TSan
 
 ["browser_aboutNewTab_bookmarksToolbarNewWindow.js"]
diff --git a/browser/base/content/test/about/browser_aboutNetError_csp_iframe.js b/browser/base/content/test/about/browser_aboutNetError_csp_iframe.js
index c8028a4cf4..d245d0cd3c 100644
--- a/browser/base/content/test/about/browser_aboutNetError_csp_iframe.js
+++ b/browser/base/content/test/about/browser_aboutNetError_csp_iframe.js
@@ -8,6 +8,10 @@ const BLOCKED_PAGE =
   "http://example.org:8000/browser/browser/base/content/test/about/csp_iframe.sjs";
 
 add_task(async function test_csp() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["security.xfocsp.hideOpenInNewWindow", false]],
+  });
+
   let { iframePageTab, blockedPageTab } = await setupPage(
     "iframe_page_csp.html",
     BLOCKED_PAGE
diff --git a/browser/base/content/test/about/browser_aboutNetError_xfo_iframe.js b/browser/base/content/test/about/browser_aboutNetError_xfo_iframe.js
index f5fd240643..2373bd8b50 100644
--- a/browser/base/content/test/about/browser_aboutNetError_xfo_iframe.js
+++ b/browser/base/content/test/about/browser_aboutNetError_xfo_iframe.js
@@ -8,6 +8,10 @@ const BLOCKED_PAGE =
   "http://example.org:8000/browser/browser/base/content/test/about/xfo_iframe.sjs";
 
 add_task(async function test_xfo_iframe() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["security.xfocsp.hideOpenInNewWindow", false]],
+  });
+
   let { iframePageTab, blockedPageTab } = await setupPage(
     "iframe_page_xfo.html",
     BLOCKED_PAGE
diff --git a/browser/base/content/test/alerts/browser.toml b/browser/base/content/test/alerts/browser.toml
index d0d56f7392..aaca2ba7dc 100644
--- a/browser/base/content/test/alerts/browser.toml
+++ b/browser/base/content/test/alerts/browser.toml
@@ -19,10 +19,6 @@ skip-if = ["os == 'win'"] # Bug 1411118
 https_first_disabled = true
 skip-if = ["os == 'win'"] # Bug 1411118
 
-["browser_notification_replace.js"]
-https_first_disabled = true
-skip-if = ["os == 'win'"] # Bug 1422928
-
 ["browser_notification_tab_switching.js"]
 https_first_disabled = true
 skip-if = ["os == 'win'"] # Bug 1243263
diff --git a/browser/base/content/test/alerts/browser_notification_close.js b/browser/base/content/test/alerts/browser_notification_close.js
index 7568f1cc2d..3fd50bed5b 100644
--- a/browser/base/content/test/alerts/browser_notification_close.js
+++ b/browser/base/content/test/alerts/browser_notification_close.js
@@ -21,17 +21,16 @@ add_task(async function test_notificationClose() {
   Services.prefs.setBoolPref("alerts.showFavicons", true);
 
   await PlacesTestUtils.addVisits(notificationURI);
-  let faviconURI = await new Promise(resolve => {
-    let uri = makeURI(
-      "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVQI12P4//8/AAX+Av7czFnnAAAAAElFTkSuQmCC"
-    );
-    PlacesUtils.favicons.setAndFetchFaviconForPage(
+  let dataURL = makeURI(
+    "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVQI12P4//8/AAX+Av7czFnnAAAAAElFTkSuQmCC"
+  );
+  await new Promise(resolve => {
+    PlacesUtils.favicons.setFaviconForPage(
       notificationURI,
-      uri,
-      true,
-      PlacesUtils.favicons.FAVICON_LOAD_NON_PRIVATE,
-      uriResult => resolve(uriResult),
-      Services.scriptSecurityManager.getSystemPrincipal()
+      dataURL,
+      dataURL,
+      null,
+      resolve
     );
   });
 
@@ -67,11 +66,7 @@ add_task(async function test_notificationClose() {
         "Body text of notification should be present"
       );
       let alertIcon = alertWindow.document.getElementById("alertIcon");
-      is(
-        alertIcon.src,
-        faviconURI.spec,
-        "Icon of notification should be present"
-      );
+      is(alertIcon.src, dataURL.spec, "Icon of notification should be present");
 
       let alertCloseButton = alertWindow.document.querySelector(".close-icon");
       is(alertCloseButton.localName, "toolbarbutton", "close button found");
diff --git a/browser/base/content/test/alerts/browser_notification_replace.js b/browser/base/content/test/alerts/browser_notification_replace.js
deleted file mode 100644
index 9c72e90ab1..0000000000
--- a/browser/base/content/test/alerts/browser_notification_replace.js
+++ /dev/null
@@ -1,66 +0,0 @@
-"use strict";
-
-let notificationURL =
-  // eslint-disable-next-line @microsoft/sdl/no-insecure-url
-  "http://example.org/browser/browser/base/content/test/alerts/file_dom_notifications.html";
-
-add_task(async function test_notificationReplace() {
-  await addNotificationPermission(notificationURL);
-
-  await BrowserTestUtils.withNewTab(
-    {
-      gBrowser,
-      url: notificationURL,
-    },
-    async function dummyTabTask(aBrowser) {
-      await SpecialPowers.spawn(aBrowser, [], async function () {
-        let win = content.window.wrappedJSObject;
-        let notification = win.showNotification1();
-        let promiseCloseEvent = ContentTaskUtils.waitForEvent(
-          notification,
-          "close"
-        );
-
-        let showEvent = await ContentTaskUtils.waitForEvent(
-          notification,
-          "show"
-        );
-        Assert.equal(
-          showEvent.target.body,
-          "Test body 1",
-          "Showed tagged notification"
-        );
-
-        let newNotification = win.showNotification2();
-        let newShowEvent = await ContentTaskUtils.waitForEvent(
-          newNotification,
-          "show"
-        );
-        Assert.equal(
-          newShowEvent.target.body,
-          "Test body 2",
-          "Showed new notification with same tag"
-        );
-
-        let closeEvent = await promiseCloseEvent;
-        Assert.equal(
-          closeEvent.target.body,
-          "Test body 1",
-          "Closed previous tagged notification"
-        );
-
-        let promiseNewCloseEvent = ContentTaskUtils.waitForEvent(
-          newNotification,
-          "close"
-        );
-        newNotification.close();
-        let newCloseEvent = await promiseNewCloseEvent;
-        Assert.equal(
-          newCloseEvent.target.body,
-          "Test body 2",
-          "Closed new notification"
-        );
-      });
-    }
-  );
-});
diff --git a/browser/base/content/test/contextMenu/browser.toml b/browser/base/content/test/contextMenu/browser.toml
index 660f6a955b..c7af1bc437 100644
--- a/browser/base/content/test/contextMenu/browser.toml
+++ b/browser/base/content/test/contextMenu/browser.toml
@@ -101,3 +101,5 @@ support-files = [
   "test_view_image_inline_svg.html",
 ]
 skip-if = ["os == 'linux' && socketprocess_networking"]
+
+["browser_contextmenu_cross_boundary_selection.js"]
diff --git a/browser/base/content/test/contextMenu/browser_contextmenu.js b/browser/base/content/test/contextMenu/browser_contextmenu.js
index 00da3113c6..d8dc0ab5e0 100644
--- a/browser/base/content/test/contextMenu/browser_contextmenu.js
+++ b/browser/base/content/test/contextMenu/browser_contextmenu.js
@@ -41,6 +41,10 @@ let hasContainers =
   Services.prefs.getBoolPref("privacy.userContext.enabled") &&
   ContextualIdentityService.getPublicIdentities().length;
 
+const hasSelectTranslations =
+  Services.prefs.getBoolPref("browser.translations.enable") &&
+  Services.prefs.getBoolPref("browser.translations.select.enable");
+
 const example_base =
   // eslint-disable-next-line @microsoft/sdl/no-insecure-url
   "http://example.com/browser/browser/base/content/test/contextMenu/";
@@ -112,6 +116,7 @@ add_task(async function test_xul_text_link_label() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 
   // Clean up so won't affect HTML element test cases.
@@ -204,6 +209,7 @@ const kLinkItems = [
   true,
   "context-searchselect-private",
   true,
+  ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
 ];
 
 add_task(async function test_link() {
@@ -234,6 +240,7 @@ add_task(async function test_mailto() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 });
 
@@ -247,6 +254,7 @@ add_task(async function test_tel() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 });
 
@@ -273,6 +281,10 @@ add_task(async function test_image() {
         null,
         "context-setDesktopBackground",
         true,
+        "---",
+        null,
+        "context-take-screenshot",
+        true,
       ],
       {
         onContextMenuShown() {
@@ -356,6 +368,10 @@ add_task(async function test_video_ok() {
     true,
     "context-sendvideo",
     true,
+    "---",
+    null,
+    "context-take-screenshot",
+    true,
   ]);
 
   await SpecialPowers.popPrefEnv();
@@ -404,6 +420,10 @@ add_task(async function test_video_ok() {
     true,
     "context-sendvideo",
     true,
+    "---",
+    null,
+    "context-take-screenshot",
+    true,
   ]);
 
   await SpecialPowers.popPrefEnv();
@@ -490,6 +510,10 @@ add_task(async function test_video_bad() {
     true,
     "context-sendvideo",
     true,
+    "---",
+    null,
+    "context-take-screenshot",
+    true,
   ]);
 
   await SpecialPowers.popPrefEnv();
@@ -538,6 +562,10 @@ add_task(async function test_video_bad() {
     true,
     "context-sendvideo",
     true,
+    "---",
+    null,
+    "context-take-screenshot",
+    true,
   ]);
 
   await SpecialPowers.popPrefEnv();
@@ -588,6 +616,10 @@ add_task(async function test_video_bad2() {
     false,
     "context-sendvideo",
     false,
+    "---",
+    null,
+    "context-take-screenshot",
+    true,
   ]);
 
   await SpecialPowers.popPrefEnv();
@@ -636,6 +668,10 @@ add_task(async function test_video_bad2() {
     false,
     "context-sendvideo",
     false,
+    "---",
+    null,
+    "context-take-screenshot",
+    true,
   ]);
 
   await SpecialPowers.popPrefEnv();
@@ -767,6 +803,10 @@ add_task(async function test_video_in_iframe() {
       true,
       "---",
       null,
+      "context-take-frame-screenshot",
+      true,
+      "---",
+      null,
       "context-viewframeinfo",
       true,
     ]),
@@ -846,6 +886,10 @@ add_task(async function test_video_in_iframe() {
       true,
       "---",
       null,
+      "context-take-frame-screenshot",
+      true,
+      "---",
+      null,
       "context-viewframeinfo",
       true,
     ]),
@@ -967,6 +1011,10 @@ add_task(async function test_image_in_iframe() {
       true,
       "---",
       null,
+      "context-take-frame-screenshot",
+      true,
+      "---",
+      null,
       "context-viewframeinfo",
       true,
     ]),
@@ -1336,6 +1384,7 @@ add_task(async function test_select_text() {
       true,
       "context-searchselect-private",
       true,
+      ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
       "---",
       null,
       "context-viewpartialsource-selection",
@@ -1369,6 +1418,9 @@ add_task(async function test_select_text_search_service_not_initialized() {
       null,
       "context-take-screenshot",
       true,
+      ...(hasSelectTranslations
+        ? ["---", null, "context-translate-selection", true]
+        : []),
       "---",
       null,
       "context-viewpartialsource-selection",
@@ -1423,6 +1475,7 @@ add_task(async function test_select_text_link() {
       true,
       "context-searchselect-private",
       true,
+      ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
       "---",
       null,
       "context-viewpartialsource-selection",
@@ -1490,6 +1543,9 @@ add_task(async function test_imagelink() {
     null,
     "context-setDesktopBackground",
     true,
+    ...(hasSelectTranslations
+      ? ["---", null, "context-translate-selection", true]
+      : []),
   ]);
 });
 
@@ -1591,6 +1647,10 @@ add_task(async function test_longdesc() {
     null,
     "context-setDesktopBackground",
     true,
+    "---",
+    null,
+    "context-take-screenshot",
+    true,
   ]);
 });
 
@@ -1682,6 +1742,7 @@ add_task(async function test_svg_link() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 
   await test_contextmenu("#svg-with-link2 > a", [
@@ -1711,6 +1772,7 @@ add_task(async function test_svg_link() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 
   await test_contextmenu("#svg-with-link3 > a", [
@@ -1740,6 +1802,7 @@ add_task(async function test_svg_link() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 });
 
@@ -1771,6 +1834,7 @@ add_task(async function test_svg_relative_link() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 
   await test_contextmenu("#svg-with-relative-link2 > a", [
@@ -1800,6 +1864,7 @@ add_task(async function test_svg_relative_link() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 
   await test_contextmenu("#svg-with-relative-link3 > a", [
@@ -1829,6 +1894,7 @@ add_task(async function test_svg_relative_link() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 });
 
@@ -1898,6 +1964,7 @@ add_task(async function test_background_image() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 
   // Don't show image related context menu commands when there is a selection
@@ -1921,6 +1988,7 @@ add_task(async function test_background_image() {
       true,
       "context-searchselect-private",
       true,
+      ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
       "---",
       null,
       "context-viewpartialsource-selection",
@@ -1989,6 +2057,7 @@ add_task(async function test_strip_on_share_on_secure_about_page() {
     true,
     "context-searchselect-private",
     true,
+    ...(hasSelectTranslations ? ["context-translate-selection", true] : []),
   ]);
 
   // Clean up
diff --git a/browser/base/content/test/contextMenu/browser_contextmenu_cross_boundary_selection.js b/browser/base/content/test/contextMenu/browser_contextmenu_cross_boundary_selection.js
new file mode 100644
index 0000000000..3137a1e136
--- /dev/null
+++ b/browser/base/content/test/contextMenu/browser_contextmenu_cross_boundary_selection.js
@@ -0,0 +1,73 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const PAGE = `
+  data:text/html,
+  <div>OuterText<div>
+  <div id="host">
+    <template shadowrootmode="open">
+      <span id="innerText">InnerText</span>
+    </template>
+  </div>
+  `;
+/**
+ * Tests that right click on a cross boundary selection shows the context menu
+ */
+add_task(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [["dom.shadowdom.selection_across_boundary.enabled", true]],
+  });
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: PAGE,
+    },
+    async function (browser) {
+      let contextMenu = document.getElementById("contentAreaContextMenu");
+      let awaitPopupShown = BrowserTestUtils.waitForEvent(
+        contextMenu,
+        "popupshown"
+      );
+
+      let awaitPopupHidden = BrowserTestUtils.waitForEvent(
+        contextMenu,
+        "popuphidden"
+      );
+
+      await SpecialPowers.spawn(browser, [], () => {
+        let host = content.document.getElementById("host");
+        content.getSelection().setBaseAndExtent(
+          content.document.body,
+          0,
+          host.shadowRoot.getElementById("innerText").firstChild,
+          3 // Only select the first three characters of the inner text
+        );
+      });
+
+      await BrowserTestUtils.synthesizeMouseAtCenter(
+        "div", // Click on the div for OuterText
+        {
+          type: "contextmenu",
+          button: 2,
+        },
+        browser
+      );
+
+      await awaitPopupShown;
+
+      const allVisibleMenuItems = Array.from(contextMenu.children)
+        .filter(elem => {
+          return !elem.hidden;
+        })
+        .map(elem => elem.id);
+
+      ok(
+        allVisibleMenuItems.includes("context-copy"),
+        "copy button should exist"
+      );
+
+      contextMenu.hidePopup();
+      await awaitPopupHidden;
+    }
+  );
+});
diff --git a/browser/base/content/test/contextMenu/browser_strip_on_share_link.js b/browser/base/content/test/contextMenu/browser_strip_on_share_link.js
index 435b1aa0ff..144076cfb2 100644
--- a/browser/base/content/test/contextMenu/browser_strip_on_share_link.js
+++ b/browser/base/content/test/contextMenu/browser_strip_on_share_link.js
@@ -97,6 +97,18 @@ add_task(async function testQueryParamIsNotStrippedForWrongSiteSpecific() {
   });
 });
 
+// Ensuring clean copy works with magnet links. We don't strip anything but copying the original URI should still work.
+add_task(async function testMagneticLinks() {
+  let originalUrl = "magnet:?xt=urn:btih:somesha1hash";
+  let shortenedUrl = "magnet:?xt=urn:btih:somesha1hash";
+  await testStripOnShare({
+    selectWholeUrl: true,
+    validUrl: originalUrl,
+    strippedUrl: shortenedUrl,
+    useTestList: true,
+  });
+});
+
 /**
  * Opens a new tab, opens the context menu and checks that the strip-on-share menu item is visible.
  * Checks that the stripped version of the url is copied to the clipboard.
diff --git a/browser/base/content/test/general/browser_documentnavigation.js b/browser/base/content/test/general/browser_documentnavigation.js
index 880db6110f..b68e6ec3f0 100644
--- a/browser/base/content/test/general/browser_documentnavigation.js
+++ b/browser/base/content/test/general/browser_documentnavigation.js
@@ -229,7 +229,7 @@ add_task(async function () {
   let sidebar = document.getElementById("sidebar");
 
   let loadPromise = BrowserTestUtils.waitForEvent(sidebar, "load", true);
-  SidebarUI.toggle("viewBookmarksSidebar");
+  SidebarController.toggle("viewBookmarksSidebar");
   await loadPromise;
 
   gURLBar.focus();
@@ -278,7 +278,7 @@ add_task(async function () {
     "back focus with sidebar urlbar"
   );
 
-  SidebarUI.toggle("viewBookmarksSidebar");
+  SidebarController.toggle("viewBookmarksSidebar");
 });
 
 // Navigate when the downloads panel is open
diff --git a/browser/base/content/test/performance/browser_preferences_usage.js b/browser/base/content/test/performance/browser_preferences_usage.js
index b0ff140d19..9ad9a8dde8 100644
--- a/browser/base/content/test/performance/browser_preferences_usage.js
+++ b/browser/base/content/test/performance/browser_preferences_usage.js
@@ -70,13 +70,6 @@ function checkPrefGetters(stats, max, knownProblematicPrefs = {}) {
     }
   }
 
-  // This pref will be accessed by mozJSComponentLoader when loading modules,
-  // which fails TV runs since they run the test multiple times without restarting.
-  // We just ignore this pref, since it's for testing only anyway.
-  if (knownProblematicPrefs["browser.startup.record"]) {
-    delete knownProblematicPrefs["browser.startup.record"];
-  }
-
   let unusedPrefs = Object.keys(knownProblematicPrefs);
   is(
     unusedPrefs.length,
@@ -104,18 +97,9 @@ add_task(async function startup() {
   let max = 40;
 
   let knownProblematicPrefs = {
-    "browser.startup.record": {
-      // This pref is accessed in Nighly and debug builds only.
-      min: 200,
-      max: 450,
-    },
     "network.loadinfo.skip_type_assertion": {
       // This is accessed in debug only.
     },
-    "chrome.override_package.global": {
-      min: 0,
-      max: 50,
-    },
   };
 
   let startupRecorder =
@@ -135,9 +119,6 @@ add_task(async function open_10_tabs() {
   const max = 4 * DEFAULT_PROCESS_COUNT;
 
   let knownProblematicPrefs = {
-    "browser.startup.record": {
-      max: 20,
-    },
     "browser.tabs.remote.logSwitchTiming": {
       max: 35,
     },
diff --git a/browser/base/content/test/popupNotifications/browser_popupNotification_security_delay.js b/browser/base/content/test/popupNotifications/browser_popupNotification_security_delay.js
index 140c2be2fd..3c652b26a2 100644
--- a/browser/base/content/test/popupNotifications/browser_popupNotification_security_delay.js
+++ b/browser/base/content/test/popupNotifications/browser_popupNotification_security_delay.js
@@ -44,22 +44,22 @@ add_setup(async function () {
   });
 });
 
+/**
+ * The security delay calculation in PopupNotification.sys.mjs is dependent on
+ * the monotonically increasing value of performance.now. This timestamp is
+ * not relative to a fixed date, but to runtime.
+ * We need to wait for the value performance.now() to be larger than the
+ * security delay in order to observe the bug. Only then does the
+ * timeSinceShown check in PopupNotifications.sys.mjs lead to a timeSinceShown
+ * value that is unconditionally greater than lazy.buttonDelay for
+ * notification.timeShown = null = 0.
+ * See: https://searchfox.org/mozilla-central/rev/f32d5f3949a3f4f185122142b29f2e3ab776836e/toolkit/modules/PopupNotifications.sys.mjs#1870-1872
+ *
+ * When running in automation as part of a larger test suite performance.now()
+ * should usually be already sufficiently high in which case this check should
+ * directly resolve.
+ */
 async function ensureSecurityDelayReady() {
-  /**
-   * The security delay calculation in PopupNotification.sys.mjs is dependent on
-   * the monotonically increasing value of performance.now. This timestamp is
-   * not relative to a fixed date, but to runtime.
-   * We need to wait for the value performance.now() to be larger than the
-   * security delay in order to observe the bug. Only then does the
-   * timeSinceShown check in PopupNotifications.sys.mjs lead to a timeSinceShown
-   * value that is unconditionally greater than lazy.buttonDelay for
-   * notification.timeShown = null = 0.
-   * See: https://searchfox.org/mozilla-central/rev/f32d5f3949a3f4f185122142b29f2e3ab776836e/toolkit/modules/PopupNotifications.sys.mjs#1870-1872
-   *
-   * When running in automation as part of a larger test suite performance.now()
-   * should usually be already sufficiently high in which case this check should
-   * directly resolve.
-   */
   await TestUtils.waitForCondition(
     () => performance.now() > TEST_SECURITY_DELAY,
     "Wait for performance.now() > SECURITY_DELAY",
@@ -69,73 +69,73 @@ async function ensureSecurityDelayReady() {
 }
 
 /**
- * Tests that when we show a second notification while the panel is open the
- * timeShown attribute is correctly set and the security delay is enforced
- * properly.
+ * Test helper for security delay tests which performs the following steps:
+ * 1. Shows a test notification.
+ * 2. Waits for the notification panel to be shown and checks that the initial
+ *    security delay blocks clicks.
+ * 3. Waits for the security delay to expire. Clicks should now be allowed.
+ * 4. Executes the provided onSecurityDelayExpired function. This function
+ *    should renew the security delay.
+ * 5. Tests that the security delay was renewed.
+ * 6. Ensures that after the security delay the notification can be closed.
+ *
+ * @param {*} options
+ * @param {function} options.onSecurityDelayExpired - Function to run after the
+ *  security delay has expired. This function should trigger a renew of the
+ *  security delay.
+ * @param {function} options.cleanupFn - Optional cleanup function to run after
+ * the test has completed.
+ * @returns {Promise<void>} - Resolves when the test has completed.
  */
-add_task(async function test_timeShownMultipleNotifications() {
+async function runPopupNotificationSecurityDelayTest({
+  onSecurityDelayExpired,
+  cleanupFn = () => {},
+}) {
   await ensureSecurityDelayReady();
 
-  ok(
-    !PopupNotifications.isPanelOpen,
-    "PopupNotification panel should not be open initially."
-  );
-
-  info("Open the first notification.");
+  info("Open a notification.");
   let popupShownPromise = waitForNotificationPanel();
   showNotification();
   await popupShownPromise;
   ok(
     PopupNotifications.isPanelOpen,
-    "PopupNotification should be open after first show call."
+    "PopupNotification should be open after show call."
   );
 
-  is(
-    PopupNotifications._currentNotifications.length,
-    1,
-    "There should only be one notification"
+  // Test that the initial security delay works.
+  info(
+    "Trigger main action via button click during the initial security delay."
   );
+  triggerMainCommand(PopupNotifications.panel);
 
+  await new Promise(resolve => setTimeout(resolve, 0));
+
+  ok(PopupNotifications.isPanelOpen, "PopupNotification should still be open.");
   let notification = PopupNotifications.getNotification(
     "foo",
     gBrowser.selectedBrowser
   );
-  is(notification?.id, "foo", "There should be a notification with id foo");
-  ok(notification.timeShown, "The notification should have timeShown set");
-
-  info(
-    "Call show again with the same notification id while the PopupNotification panel is still open."
-  );
-  showNotification();
   ok(
-    PopupNotifications.isPanelOpen,
-    "PopupNotification should still open after second show call."
-  );
-  notification = PopupNotifications.getNotification(
-    "foo",
-    gBrowser.selectedBrowser
-  );
-  is(
-    PopupNotifications._currentNotifications.length,
-    1,
-    "There should still only be one notification"
+    notification,
+    "Notification should still be open because we clicked during the security delay."
   );
+  // If the notification is no longer shown (test failure) skip the remaining
+  // checks.
+  if (!notification) {
+    await cleanupFn();
+    return;
+  }
 
-  is(
-    notification?.id,
-    "foo",
-    "There should still be a notification with id foo"
+  info("Wait for security delay to expire.");
+  await new Promise(resolve =>
+    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+    setTimeout(resolve, TEST_SECURITY_DELAY + 500)
   );
-  ok(notification.timeShown, "The notification should have timeShown set");
 
-  let notificationHiddenPromise = waitForNotificationPanelHidden();
-
-  info("Trigger main action via button click during security delay");
-
-  // Wait for a tick of the event loop to ensure the button we're clicking
-  // has been slotted into moz-button-group
-  await new Promise(resolve => setTimeout(resolve, 0));
+  info("Run test specific actions which restarts the security delay.");
+  await onSecurityDelayExpired();
 
+  info("Trigger main action via button click during the new security delay.");
   triggerMainCommand(PopupNotifications.panel);
 
   await new Promise(resolve => setTimeout(resolve, 0));
@@ -149,10 +149,10 @@ add_task(async function test_timeShownMultipleNotifications() {
     notification,
     "Notification should still be open because we clicked during the security delay."
   );
-
   // If the notification is no longer shown (test failure) skip the remaining
   // checks.
   if (!notification) {
+    await cleanupFn();
     return;
   }
 
@@ -163,6 +163,7 @@ add_task(async function test_timeShownMultipleNotifications() {
   notification.timeShown = performance.now() - fakeTimeShown;
 
   info("Trigger main action via button click outside security delay");
+  let notificationHiddenPromise = waitForNotificationPanelHidden();
   triggerMainCommand(PopupNotifications.panel);
 
   info("Wait for panel to be hidden.");
@@ -170,15 +171,19 @@ add_task(async function test_timeShownMultipleNotifications() {
 
   ok(
     !PopupNotifications.getNotification("foo", gBrowser.selectedBrowser),
-    "Should not longer see the notification."
+    "Should no longer see the notification."
   );
-});
+
+  info("Cleanup.");
+  await cleanupFn();
+}
 
 /**
- * Tests that when we reshow a notification after a tab switch the timeShown
- * attribute is correctly reset and the security delay is enforced.
+ * Tests that when we show a second notification while the panel is open the
+ * timeShown attribute is correctly set and the security delay is enforced
+ * properly.
  */
-add_task(async function test_notificationReshowTabSwitch() {
+add_task(async function test_timeShownMultipleNotifications() {
   await ensureSecurityDelayReady();
 
   ok(
@@ -195,6 +200,12 @@ add_task(async function test_notificationReshowTabSwitch() {
     "PopupNotification should be open after first show call."
   );
 
+  is(
+    PopupNotifications._currentNotifications.length,
+    1,
+    "There should only be one notification"
+  );
+
   let notification = PopupNotifications.getNotification(
     "foo",
     gBrowser.selectedBrowser
@@ -202,69 +213,39 @@ add_task(async function test_notificationReshowTabSwitch() {
   is(notification?.id, "foo", "There should be a notification with id foo");
   ok(notification.timeShown, "The notification should have timeShown set");
 
-  info("Trigger main action via button click during security delay");
-  triggerMainCommand(PopupNotifications.panel);
-
-  await new Promise(resolve => setTimeout(resolve, 0));
-
-  ok(PopupNotifications.isPanelOpen, "PopupNotification should still be open.");
-  notification = PopupNotifications.getNotification(
-    "foo",
-    gBrowser.selectedBrowser
-  );
-  ok(
-    notification,
-    "Notification should still be open because we clicked during the security delay."
-  );
-
-  // If the notification is no longer shown (test failure) skip the remaining
-  // checks.
-  if (!notification) {
-    return;
-  }
-
-  let panelHiddenPromise = waitForNotificationPanelHidden();
-  let panelShownPromise;
-
-  info("Open a new tab which hides the notification panel.");
-  await BrowserTestUtils.withNewTab("https://example.com", async () => {
-    info("Wait for panel to be hidden by tab switch.");
-    await panelHiddenPromise;
-    info(
-      "Keep the tab open until the security delay for the original notification show has expired."
-    );
-    await new Promise(resolve =>
-      // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
-      setTimeout(resolve, TEST_SECURITY_DELAY + 500)
-    );
-
-    panelShownPromise = waitForNotificationPanel();
-  });
   info(
-    "Wait for the panel to show again after the tab close. We're showing the original tab again."
+    "Call show again with the same notification id while the PopupNotification panel is still open."
   );
-  await panelShownPromise;
-
+  showNotification();
   ok(
     PopupNotifications.isPanelOpen,
-    "PopupNotification should be shown after tab close."
+    "PopupNotification should still open after second show call."
   );
   notification = PopupNotifications.getNotification(
     "foo",
     gBrowser.selectedBrowser
   );
   is(
+    PopupNotifications._currentNotifications.length,
+    1,
+    "There should still only be one notification"
+  );
+
+  is(
     notification?.id,
     "foo",
     "There should still be a notification with id foo"
   );
+  ok(notification.timeShown, "The notification should have timeShown set");
 
   let notificationHiddenPromise = waitForNotificationPanelHidden();
 
-  info(
-    "Because we re-show the panel after tab close / switch the security delay should have reset."
-  );
-  info("Trigger main action via button click during the new security delay.");
+  info("Trigger main action via button click during security delay");
+
+  // Wait for a tick of the event loop to ensure the button we're clicking
+  // has been slotted into moz-button-group
+  await new Promise(resolve => setTimeout(resolve, 0));
+
   triggerMainCommand(PopupNotifications.panel);
 
   await new Promise(resolve => setTimeout(resolve, 0));
@@ -278,6 +259,7 @@ add_task(async function test_notificationReshowTabSwitch() {
     notification,
     "Notification should still be open because we clicked during the security delay."
   );
+
   // If the notification is no longer shown (test failure) skip the remaining
   // checks.
   if (!notification) {
@@ -298,109 +280,83 @@ add_task(async function test_notificationReshowTabSwitch() {
 
   ok(
     !PopupNotifications.getNotification("foo", gBrowser.selectedBrowser),
-    "Should not longer see the notification."
+    "Should no longer see the notification."
   );
 });
 
 /**
+ * Tests that when we reshow a notification after a tab switch the timeShown
+ * attribute is correctly reset and the security delay is enforced.
+ */
+add_task(async function test_notificationReshowTabSwitch() {
+  await runPopupNotificationSecurityDelayTest({
+    onSecurityDelayExpired: async () => {
+      let panelHiddenPromise = waitForNotificationPanelHidden();
+      let panelShownPromise;
+
+      info("Open a new tab which hides the notification panel.");
+      await BrowserTestUtils.withNewTab("https://example.com", async () => {
+        info("Wait for panel to be hidden by tab switch.");
+        await panelHiddenPromise;
+        panelShownPromise = waitForNotificationPanel();
+      });
+      info(
+        "Wait for the panel to show again after the tab close. We're showing the original tab again."
+      );
+      await panelShownPromise;
+
+      ok(
+        PopupNotifications.isPanelOpen,
+        "PopupNotification should be shown after tab close."
+      );
+      let notification = PopupNotifications.getNotification(
+        "foo",
+        gBrowser.selectedBrowser
+      );
+      is(
+        notification?.id,
+        "foo",
+        "There should still be a notification with id foo"
+      );
+
+      info(
+        "Because we re-show the panel after tab close / switch the security delay should have reset."
+      );
+    },
+  });
+});
+
+/**
  * Tests that the security delay gets reset when a window is repositioned and
  * the PopupNotifications panel position is updated.
  */
 add_task(async function test_notificationWindowMove() {
-  await ensureSecurityDelayReady();
-
-  info("Open a notification.");
-  let popupShownPromise = waitForNotificationPanel();
-  showNotification();
-  await popupShownPromise;
-  ok(
-    PopupNotifications.isPanelOpen,
-    "PopupNotification should be open after show call."
-  );
-
-  // Test that the initial security delay works.
-  info("Trigger main action via button click during the new security delay.");
-  triggerMainCommand(PopupNotifications.panel);
-
-  await new Promise(resolve => setTimeout(resolve, 0));
-
-  ok(PopupNotifications.isPanelOpen, "PopupNotification should still be open.");
-  let notification = PopupNotifications.getNotification(
-    "foo",
-    gBrowser.selectedBrowser
-  );
-  ok(
-    notification,
-    "Notification should still be open because we clicked during the security delay."
-  );
-  // If the notification is no longer shown (test failure) skip the remaining
-  // checks.
-  if (!notification) {
-    return;
-  }
-
-  info("Wait for security delay to expire.");
-  await new Promise(resolve =>
-    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
-    setTimeout(resolve, TEST_SECURITY_DELAY + 500)
-  );
-
-  info("Reposition the window");
-  // Remember original window position.
-  let { screenX, screenY } = window;
-
-  let promisePopupPositioned = BrowserTestUtils.waitForEvent(
-    PopupNotifications.panel,
-    "popuppositioned"
-  );
-
-  // Move the window.
-  window.moveTo(200, 200);
-
-  // Wait for the panel to reposition and the PopupNotifications listener to run.
-  await promisePopupPositioned;
-  await new Promise(resolve => setTimeout(resolve, 0));
-
-  info("Trigger main action via button click during the new security delay.");
-  triggerMainCommand(PopupNotifications.panel);
-
-  await new Promise(resolve => setTimeout(resolve, 0));
-
-  ok(PopupNotifications.isPanelOpen, "PopupNotification should still be open.");
-  notification = PopupNotifications.getNotification(
-    "foo",
-    gBrowser.selectedBrowser
-  );
-  ok(
-    notification,
-    "Notification should still be open because we clicked during the security delay."
-  );
-  // If the notification is no longer shown (test failure) skip the remaining
-  // checks.
-  if (!notification) {
-    return;
-  }
-
-  // Ensure that once the security delay has passed the notification can be
-  // closed again.
-  let fakeTimeShown = TEST_SECURITY_DELAY + 500;
-  info(`Manually set timeShown to ${fakeTimeShown}ms in the past.`);
-  notification.timeShown = performance.now() - fakeTimeShown;
-
-  info("Trigger main action via button click outside security delay");
-  let notificationHiddenPromise = waitForNotificationPanelHidden();
-  triggerMainCommand(PopupNotifications.panel);
-
-  info("Wait for panel to be hidden.");
-  await notificationHiddenPromise;
-
-  ok(
-    !PopupNotifications.getNotification("foo", gBrowser.selectedBrowser),
-    "Should not longer see the notification."
-  );
-
-  // Reset window position
-  window.moveTo(screenX, screenY);
+  let screenX, screenY;
+
+  await runPopupNotificationSecurityDelayTest({
+    onSecurityDelayExpired: async () => {
+      info("Reposition the window");
+      // Remember original window position.
+      screenX = window.screenX;
+      screenY = window.screenY;
+
+      let promisePopupPositioned = BrowserTestUtils.waitForEvent(
+        PopupNotifications.panel,
+        "popuppositioned"
+      );
+
+      // Move the window.
+      window.moveTo(200, 200);
+
+      // Wait for the panel to reposition and the PopupNotifications listener to run.
+      await promisePopupPositioned;
+      await new Promise(resolve => setTimeout(resolve, 0));
+    },
+    cleanupFn: async () => {
+      // Reset window position
+      window.moveTo(screenX, screenY);
+    },
+  });
 });
 
 /**
@@ -563,5 +519,49 @@ add_task(async function test_notificationDuringFullScreenTransition() {
     info("Wait for full screen transition end.");
     await promiseFullScreenTransitionEnd;
     info("Full screen transition end");
+
+    await SpecialPowers.popPrefEnv();
+  });
+});
+
+/**
+ * Tests that the security delay gets extended when pointer lock is entered.
+ */
+add_task(async function test_notificationPointerLock() {
+  // We need a tab to enter pointer lock.
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    "https://example.com"
+  );
+
+  await runPopupNotificationSecurityDelayTest({
+    onSecurityDelayExpired: async () => {
+      info("Enter pointer lock");
+      // Move focus to the browser to ensure pointer lock request succeeds.
+      gBrowser.selectedBrowser.focus();
+      let pointerLockEnterPromise = TestUtils.topicObserved(
+        "pointer-lock-entered"
+      );
+      await SpecialPowers.spawn(gBrowser.selectedBrowser, [], async () => {
+        SpecialPowers.wrap(content.document).notifyUserGestureActivation();
+        await content.document.body.requestPointerLock();
+      });
+
+      // Wait for pointer lock to be entered and the PopupNotifications listener to run.
+      await pointerLockEnterPromise;
+      await new Promise(resolve => setTimeout(resolve, 0));
+    },
+    cleanupFn: async () => {
+      // Cleanup.
+      await SpecialPowers.spawn(gBrowser.selectedBrowser, [], async () => {
+        SpecialPowers.wrap(content.document).notifyUserGestureActivation();
+        await content.document.exitPointerLock();
+      });
+      await TestUtils.waitForCondition(
+        () => !window.PointerLock.isActive,
+        "Wait for pointer lock exit."
+      );
+      BrowserTestUtils.removeTab(tab);
+    },
   });
 });
diff --git a/browser/base/content/test/sidebar/browser_sidebar_adopt.js b/browser/base/content/test/sidebar/browser_sidebar_adopt.js
index 344a71cb9b..988ac1487f 100644
--- a/browser/base/content/test/sidebar/browser_sidebar_adopt.js
+++ b/browser/base/content/test/sidebar/browser_sidebar_adopt.js
@@ -5,7 +5,7 @@
  * during the initial browser startup - but it would be hard to do with a mochitest. */
 
 registerCleanupFunction(() => {
-  SidebarUI.hide();
+  SidebarController.hide();
 });
 
 function failIfSidebarFocusedFires() {
@@ -26,7 +26,7 @@ add_task(async function testAdoptedTwoWindows() {
   info("Ensure that sidebar state is adopted only from the opener");
 
   let win1 = await BrowserTestUtils.openNewBrowserWindow();
-  await win1.SidebarUI.show("viewBookmarksSidebar");
+  await win1.SidebarController.show("viewBookmarksSidebar");
   await BrowserTestUtils.closeWindow(win1);
 
   let win2 = await BrowserTestUtils.openNewBrowserWindow();
@@ -34,7 +34,7 @@ add_task(async function testAdoptedTwoWindows() {
     !win2.document.getElementById("sidebar-button").hasAttribute("checked"),
     "Sidebar button isn't checked"
   );
-  ok(!win2.SidebarUI.isOpen, "Sidebar is closed");
+  ok(!win2.SidebarController.isOpen, "Sidebar is closed");
   await BrowserTestUtils.closeWindow(win2);
 });
 
@@ -46,7 +46,7 @@ add_task(async function testEventsReceivedInMainWindow() {
   let initialShown = BrowserTestUtils.waitForEvent(window, "SidebarShown");
   let initialFocus = BrowserTestUtils.waitForEvent(window, "SidebarFocused");
 
-  await SidebarUI.show("viewBookmarksSidebar");
+  await SidebarController.show("viewBookmarksSidebar");
   await initialShown;
   await initialFocus;
 
diff --git a/browser/base/content/test/sidebar/browser_sidebar_app_locale_changed.js b/browser/base/content/test/sidebar/browser_sidebar_app_locale_changed.js
index 5b07da9839..1e52895a7d 100644
--- a/browser/base/content/test/sidebar/browser_sidebar_app_locale_changed.js
+++ b/browser/base/content/test/sidebar/browser_sidebar_app_locale_changed.js
@@ -8,7 +8,7 @@
 
 add_task(function cleanup() {
   registerCleanupFunction(() => {
-    SidebarUI.hide();
+    SidebarController.hide();
   });
 });
 
@@ -17,7 +17,7 @@ add_task(function cleanup() {
  */
 async function testLiveReloading(sidebarName) {
   info("Showing the sidebar " + sidebarName);
-  await SidebarUI.show(sidebarName);
+  await SidebarController.show(sidebarName);
 
   function getTreeChildren() {
     const sidebarDoc =
@@ -44,7 +44,7 @@ async function testLiveReloading(sidebarName) {
   );
 
   info("Hiding the sidebar");
-  SidebarUI.hide();
+  SidebarController.hide();
 }
 
 add_task(async function test_bookmarks_sidebar() {
diff --git a/browser/base/content/test/sidebar/browser_sidebar_keys.js b/browser/base/content/test/sidebar/browser_sidebar_keys.js
index f12d1cf5f7..61e4ce9737 100644
--- a/browser/base/content/test/sidebar/browser_sidebar_keys.js
+++ b/browser/base/content/test/sidebar/browser_sidebar_keys.js
@@ -11,11 +11,11 @@ async function testSidebarKeyToggle(key, options, expectedSidebarId) {
     expectedSidebarId
   );
   EventUtils.synthesizeKey(key, options);
-  Assert.ok(!SidebarUI.isOpen);
+  Assert.ok(!SidebarController.isOpen);
 }
 
 add_task(async function test_sidebar_keys() {
-  registerCleanupFunction(() => SidebarUI.hide());
+  registerCleanupFunction(() => SidebarController.hide());
 
   await testSidebarKeyToggle("b", { accelKey: true }, "viewBookmarksSidebar");
 
@@ -30,7 +30,7 @@ add_task(async function test_sidebar_in_customize_mode() {
   let { CustomizableUI } = ChromeUtils.importESModule(
     "resource:///modules/CustomizableUI.sys.mjs"
   );
-  registerCleanupFunction(() => SidebarUI.hide());
+  registerCleanupFunction(() => SidebarController.hide());
 
   let placement = CustomizableUI.getPlacementOfWidget("sidebar-button");
   if (!(placement?.area == CustomizableUI.AREA_NAVBAR)) {
@@ -55,7 +55,7 @@ add_task(async function test_sidebar_in_customize_mode() {
     ).a;
 
   let promiseShown = BrowserTestUtils.waitForEvent(window, "SidebarShown");
-  SidebarUI.show("viewBookmarksSidebar");
+  SidebarController.show("viewBookmarksSidebar");
   await promiseShown;
 
   Assert.greater(
@@ -80,8 +80,8 @@ add_task(async function test_sidebar_in_customize_mode() {
   );
 
   // Attempt toggle - should fail in customize mode.
-  await SidebarUI.toggle();
-  ok(SidebarUI.isOpen, "Sidebar is still open");
+  await SidebarController.toggle();
+  ok(SidebarController.isOpen, "Sidebar is still open");
 
   // Exit customize mode. This should re-enable the toggle and make the sidebar
   // toggle widget appear checked again, since toggle() didn't hide the sidebar.
@@ -98,8 +98,8 @@ add_task(async function test_sidebar_in_customize_mode() {
     "Sidebar widget background should appear checked again"
   );
 
-  await SidebarUI.toggle();
-  ok(!SidebarUI.isOpen, "Sidebar is closed");
+  await SidebarController.toggle();
+  ok(!SidebarController.isOpen, "Sidebar is closed");
   Assert.equal(
     getBGAlpha(),
     0,
diff --git a/browser/base/content/test/sidebar/browser_sidebar_move.js b/browser/base/content/test/sidebar/browser_sidebar_move.js
index d434b3bbd8..05ea9e3322 100644
--- a/browser/base/content/test/sidebar/browser_sidebar_move.js
+++ b/browser/base/content/test/sidebar/browser_sidebar_move.js
@@ -1,17 +1,17 @@
 registerCleanupFunction(() => {
   Services.prefs.clearUserPref("sidebar.position_start");
-  SidebarUI.hide();
+  SidebarController.hide();
 });
 
 const EXPECTED_START_ORDINALS = [
-  ["sidebar-launcher", 1],
+  ["sidebar-main", 1],
   ["sidebar-box", 2],
   ["sidebar-splitter", 3],
   ["appcontent", 4],
 ];
 
 const EXPECTED_END_ORDINALS = [
-  ["sidebar-launcher", 5],
+  ["sidebar-main", 5],
   ["sidebar-box", 4],
   ["sidebar-splitter", 3],
   ["appcontent", 2],
@@ -25,8 +25,8 @@ function getBrowserChildrenWithOrdinals() {
 }
 
 add_task(async function () {
-  await SidebarUI.show("viewBookmarksSidebar");
-  SidebarUI.showSwitcherPanel();
+  await SidebarController.show("viewBookmarksSidebar");
+  SidebarController.showSwitcherPanel();
 
   let reversePositionButton = document.getElementById(
     "sidebar-reverse-position"
@@ -43,8 +43,8 @@ add_task(async function () {
   ok(!box.hasAttribute("positionend"), "Positioned start");
 
   // Moved to right
-  SidebarUI.reversePosition();
-  SidebarUI.showSwitcherPanel();
+  SidebarController.reversePosition();
+  SidebarController.showSwitcherPanel();
   Assert.deepEqual(
     getBrowserChildrenWithOrdinals(),
     EXPECTED_END_ORDINALS,
@@ -58,8 +58,8 @@ add_task(async function () {
   ok(box.hasAttribute("positionend"), "Positioned end");
 
   // Moved to back to left
-  SidebarUI.reversePosition();
-  SidebarUI.showSwitcherPanel();
+  SidebarController.reversePosition();
+  SidebarController.showSwitcherPanel();
   Assert.deepEqual(
     getBrowserChildrenWithOrdinals(),
     EXPECTED_START_ORDINALS,
diff --git a/browser/base/content/test/sidebar/browser_sidebar_persist.js b/browser/base/content/test/sidebar/browser_sidebar_persist.js
index fe67bed9e0..4977c7ef0f 100644
--- a/browser/base/content/test/sidebar/browser_sidebar_persist.js
+++ b/browser/base/content/test/sidebar/browser_sidebar_persist.js
@@ -18,7 +18,7 @@ add_task(async function persist_sidebar_width() {
   {
     info("Showing new window and setting sidebar box");
     const win = await BrowserTestUtils.openNewBrowserWindow();
-    await win.SidebarUI.show("viewBookmarksSidebar");
+    await win.SidebarController.show("viewBookmarksSidebar");
     win.document.getElementById("sidebar-box").style.width = "100px";
     await BrowserTestUtils.closeWindow(win);
   }
@@ -26,7 +26,7 @@ add_task(async function persist_sidebar_width() {
   {
     info("Showing new window and seeing persisted width");
     const win = await BrowserTestUtils.openNewBrowserWindow();
-    await win.SidebarUI.show("viewBookmarksSidebar");
+    await win.SidebarController.show("viewBookmarksSidebar");
     is(
       win.document.getElementById("sidebar-box").style.width,
       "100px",
diff --git a/browser/base/content/test/sidebar/browser_sidebar_switcher.js b/browser/base/content/test/sidebar/browser_sidebar_switcher.js
index 032c23b029..0fc9e18e01 100644
--- a/browser/base/content/test/sidebar/browser_sidebar_switcher.js
+++ b/browser/base/content/test/sidebar/browser_sidebar_switcher.js
@@ -1,5 +1,5 @@
 registerCleanupFunction(() => {
-  SidebarUI.hide();
+  SidebarController.hide();
 });
 
 /**
@@ -9,14 +9,14 @@ registerCleanupFunction(() => {
  */
 function showSwitcherPanelPromise() {
   return new Promise(resolve => {
-    SidebarUI._switcherPanel.addEventListener(
+    SidebarController._switcherPanel.addEventListener(
       "popupshown",
       () => {
         resolve();
       },
       { once: true }
     );
-    SidebarUI.showSwitcherPanel();
+    SidebarController.showSwitcherPanel();
   });
 }
 
@@ -25,7 +25,10 @@ function showSwitcherPanelPromise() {
  * @returns Promise which resolves when the popup menu is opened
  */
 async function waitForSwitcherPopupShown() {
-  return BrowserTestUtils.waitForEvent(SidebarUI._switcherPanel, "popupshown");
+  return BrowserTestUtils.waitForEvent(
+    SidebarController._switcherPanel,
+    "popupshown"
+  );
 }
 
 /**
@@ -63,7 +66,7 @@ async function testSidebarMenuKeyToggle(key, sidebarTitle) {
   info(`Testing "${key}" key handling of sidebar menu popup items
   to access ${sidebarTitle} sidebar`);
 
-  Assert.ok(SidebarUI.isOpen, "Sidebar is open");
+  Assert.ok(SidebarController.isOpen, "Sidebar is open");
 
   let sidebarSwitcher = document.querySelector("#sidebar-switcher-target");
   let sidebar = document.getElementById("sidebar");
@@ -89,7 +92,7 @@ async function testSidebarMenuKeyToggle(key, sidebarTitle) {
     "The sidebar switcher target button is focused"
   );
   Assert.equal(
-    SidebarUI._switcherPanel.state,
+    SidebarController._switcherPanel.state,
     "closed",
     "Sidebar menu popup is closed"
   );
@@ -102,7 +105,7 @@ async function testSidebarMenuKeyToggle(key, sidebarTitle) {
   await promisePopupShown;
 
   Assert.equal(
-    SidebarUI._switcherPanel.state,
+    SidebarController._switcherPanel.state,
     "open",
     "Sidebar menu popup is open"
   );
@@ -111,7 +114,7 @@ async function testSidebarMenuKeyToggle(key, sidebarTitle) {
 
   let arrowDown = async (menuitemId, msg) => {
     let menuItemActive = BrowserTestUtils.waitForEvent(
-      SidebarUI._switcherPanel,
+      SidebarController._switcherPanel,
       "DOMMenuItemActive"
     );
     EventUtils.synthesizeKey("KEY_ArrowDown", {});
@@ -149,18 +152,18 @@ async function testSidebarMenuKeyToggle(key, sidebarTitle) {
   info("Testing keyboard navigation when a sidebar menu popup is closed");
 
   Assert.equal(
-    SidebarUI._switcherPanel.state,
+    SidebarController._switcherPanel.state,
     "closed",
     "Sidebar menu popup is closed"
   );
   // Test the sidebar panel is updated
   Assert.equal(
-    SidebarUI._box.getAttribute("sidebarcommand"),
+    SidebarController._box.getAttribute("sidebarcommand"),
     `view${sidebarTitle}Sidebar` /* e.g. "viewHistorySidebar" */,
     `${sidebarTitle} sidebar loaded`
   );
   Assert.equal(
-    SidebarUI.currentID,
+    SidebarController.currentID,
     `view${sidebarTitle}Sidebar` /* e.g. "viewHistorySidebar" */,
     `${sidebarTitle}'s current ID is updated to a target view`
   );
@@ -173,7 +176,7 @@ add_task(async function markup() {
       false,
       "Unexpected sidebar found - a previous test failed to cleanup correctly"
     );
-    SidebarUI.hide();
+    SidebarController.hide();
   }
 
   let sidebarPopup = document.querySelector("#sidebarMenu-popup");
@@ -205,7 +208,7 @@ add_task(async function markup() {
 
   info("Test dynamic changes in the markup of the sidebar switcher control");
 
-  await SidebarUI.show("viewBookmarksSidebar");
+  await SidebarController.show("viewBookmarksSidebar");
   await showSwitcherPanelPromise();
 
   Assert.equal(
@@ -229,25 +232,25 @@ add_task(async function markup() {
     "Sidebar switcher button is collapsed when a sidebar menu is dismissed"
   );
 
-  SidebarUI.hide();
+  SidebarController.hide();
 });
 
 add_task(async function keynav() {
   // If a sidebar is already open, close it.
-  if (SidebarUI.isOpen) {
+  if (SidebarController.isOpen) {
     Assert.ok(
       false,
       "Unexpected sidebar found - a previous test failed to cleanup correctly"
     );
-    SidebarUI.hide();
+    SidebarController.hide();
   }
 
-  await SidebarUI.show("viewBookmarksSidebar");
+  await SidebarController.show("viewBookmarksSidebar");
 
   await testSidebarMenuKeyToggle("KEY_Enter", "History");
   await testSidebarMenuKeyToggle(" ", "Tabs");
 
-  SidebarUI.hide();
+  SidebarController.hide();
 });
 
 add_task(async function mouse() {
@@ -257,11 +260,11 @@ add_task(async function mouse() {
       false,
       "Unexpected sidebar found - a previous test failed to cleanup correctly"
     );
-    SidebarUI.hide();
+    SidebarController.hide();
   }
 
   let sidebar = document.querySelector("#sidebar-box");
-  await SidebarUI.show("viewBookmarksSidebar");
+  await SidebarController.show("viewBookmarksSidebar");
 
   await showSwitcherPanelPromise();
   await pickSwitcherMenuitem("#sidebar-switcher-history");
diff --git a/browser/base/content/test/static/browser_all_files_referenced.js b/browser/base/content/test/static/browser_all_files_referenced.js
index d73c3fe8de..9668288181 100644
--- a/browser/base/content/test/static/browser_all_files_referenced.js
+++ b/browser/base/content/test/static/browser_all_files_referenced.js
@@ -276,12 +276,6 @@ var allowlist = [
   // find the references)
   { file: "chrome://browser/content/screenshots/copied-notification.svg" },
 
-  // Bug 1875361
-  { file: "chrome://global/content/ml/SummarizerModel.sys.mjs" },
-
-  // Bug 1886130
-  { file: "chrome://global/content/ml/ModelHub.sys.mjs" },
-
   // toolkit/xre/MacRunFromDmgUtils.mm
   { file: "resource://gre/localization/en-US/toolkit/global/run-from-dmg.ftl" },
 
@@ -290,6 +284,12 @@ var allowlist = [
   { file: "chrome://browser/content/screenshots/copy.svg" },
   { file: "chrome://browser/content/screenshots/download.svg" },
   { file: "chrome://browser/content/screenshots/download-white.svg" },
+
+  // Referenced programmatically
+  { file: "chrome://browser/content/backup/BackupManifest.1.schema.json" },
+
+  // Bug 1892002
+  { file: "resource://app/modules/TopSites.sys.mjs" },
 ];
 
 if (AppConstants.NIGHTLY_BUILD) {
@@ -301,6 +301,10 @@ if (AppConstants.NIGHTLY_BUILD) {
       // A debug tool that is only available in Nightly builds, and is accessed
       // directly by developers via the chrome URI (bug 1888491)
       { file: "chrome://browser/content/backup/debug.html" },
+
+      // The Transformers.js prod lib is not used in Nightly builds
+      { file: "chrome://global/content/ml/transformers.js" },
+      { file: "chrome://global/content/ml/ort.js" },
     ]
   );
 }
diff --git a/browser/base/content/test/static/browser_parsable_css.js b/browser/base/content/test/static/browser_parsable_css.js
index fb91da578a..6b075fc98f 100644
--- a/browser/base/content/test/static/browser_parsable_css.js
+++ b/browser/base/content/test/static/browser_parsable_css.js
@@ -36,6 +36,12 @@ let ignoreList = [
     errorMessage: /Unknown property.*overflow-clip-box/i,
     isFromDevTools: false,
   },
+  // content: -moz-alt-content is UA-only.
+  {
+    sourceName: /\b(html)\.css$/i,
+    errorMessage: /Error in parsing value for ‘content’/i,
+    isFromDevTools: false,
+  },
   // These variables are declared somewhere else, and error when we load the
   // files directly. They're all marked intermittent because their appearance
   // in the error console seems to not be consistent.
diff --git a/browser/base/content/test/static/browser_parsable_script.js b/browser/base/content/test/static/browser_parsable_script.js
index 3d8fbc1535..71a2930ddc 100644
--- a/browser/base/content/test/static/browser_parsable_script.js
+++ b/browser/base/content/test/static/browser_parsable_script.js
@@ -19,6 +19,7 @@ const kESModuleList = new Set([
   /browser\/vpn-card.js$/,
   /toolkit\/content\/global\/certviewer\/components\/.*\.js$/,
   /toolkit\/content\/global\/certviewer\/.*\.js$/,
+  /toolkit\/content\/global\/ml\/transformers.*\.js$/,
   /chrome\/pdfjs\/content\/web\/.*\.js$/,
 ]);
 
diff --git a/browser/base/content/test/static/browser_sentence_case_strings.js b/browser/base/content/test/static/browser_sentence_case_strings.js
index e995f76b1a..12952c9600 100644
--- a/browser/base/content/test/static/browser_sentence_case_strings.js
+++ b/browser/base/content/test/static/browser_sentence_case_strings.js
@@ -103,7 +103,7 @@ function checkSubheaders(view) {
 }
 
 async function checkUpdateBanner(view) {
-  let banner = view.querySelector("#appMenu-proton-update-banner");
+  let banner = view.querySelector("#appMenu-update-banner");
 
   const notifications = [
     "update-downloading",
diff --git a/browser/base/content/test/sync/browser_contextmenu_sendpage.js b/browser/base/content/test/sync/browser_contextmenu_sendpage.js
index a80cf8a1d0..14b5f72860 100644
--- a/browser/base/content/test/sync/browser_contextmenu_sendpage.js
+++ b/browser/base/content/test/sync/browser_contextmenu_sendpage.js
@@ -93,47 +93,44 @@ add_task(async function test_link_contextmenu() {
     "context-sendlinktodevice-popup"
   );
 
-  let expectedArray = ["context-openlinkintab"];
-
-  if (
+  const expectOpenLinkInUserContextMenu =
     Services.prefs.getBoolPref("privacy.userContext.enabled") &&
-    ContextualIdentityService.getPublicIdentities().length
-  ) {
-    expectedArray.push("context-openlinkinusercontext-menu");
-  }
+    ContextualIdentityService.getPublicIdentities().length;
+
+  const expectStripOnShareLink = Services.prefs.getBoolPref(
+    "privacy.query_stripping.strip_on_share.enabled"
+  );
+
+  const expectTranslateSelection =
+    Services.prefs.getBoolPref("browser.translations.enable") &&
+    Services.prefs.getBoolPref("browser.translations.select.enable");
 
-  expectedArray.push(
+  const expectInspectAccessibility =
+    Services.prefs.getBoolPref("devtools.accessibility.enabled", true) &&
+    (Services.prefs.getBoolPref("devtools.everOpened", false) ||
+      Services.prefs.getIntPref("devtools.selfxss.count", 0) > 0);
+
+  const expectedArray = [
+    "context-openlinkintab",
+    ...(expectOpenLinkInUserContextMenu
+      ? ["context-openlinkinusercontext-menu"]
+      : []),
     "context-openlink",
     "context-openlinkprivate",
     "context-sep-open",
     "context-bookmarklink",
     "context-savelink",
     "context-savelinktopocket",
-    "context-copylink"
-  );
-
-  if (
-    Services.prefs.getBoolPref("privacy.query_stripping.strip_on_share.enabled")
-  ) {
-    expectedArray.push("context-stripOnShareLink");
-  }
-
-  expectedArray.push(
+    "context-copylink",
+    ...(expectStripOnShareLink ? ["context-stripOnShareLink"] : []),
     "context-sendlinktodevice",
     "context-sep-sendlinktodevice",
     "context-searchselect",
-    "frame-sep"
-  );
-
-  if (
-    Services.prefs.getBoolPref("devtools.accessibility.enabled", true) &&
-    (Services.prefs.getBoolPref("devtools.everOpened", false) ||
-      Services.prefs.getIntPref("devtools.selfxss.count", 0) > 0)
-  ) {
-    expectedArray.push("context-inspect-a11y");
-  }
-
-  expectedArray.push("context-inspect");
+    ...(expectTranslateSelection ? ["context-translate-selection"] : []),
+    "frame-sep",
+    ...(expectInspectAccessibility ? ["context-inspect-a11y"] : []),
+    "context-inspect",
+  ];
 
   let menu = document.getElementById("contentAreaContextMenu");
 
diff --git a/browser/base/content/test/sync/browser_sync.js b/browser/base/content/test/sync/browser_sync.js
index 8f687842a4..03077ea67c 100644
--- a/browser/base/content/test/sync/browser_sync.js
+++ b/browser/base/content/test/sync/browser_sync.js
@@ -607,17 +607,20 @@ add_task(async function test_experiment_ui_state_unconfigured() {
   checkFxAAvatar("not_configured");
 
   let expectedLabel = gSync.fluentStrings.formatValueSync(
-    "appmenuitem-sign-in-account"
+    "synced-tabs-fxa-sign-in"
+  );
+
+  let expectedDescriptionLabel = gSync.fluentStrings.formatValueSync(
+    "fxa-menu-sync-description"
   );
 
   await openMainPanel();
 
   checkFxaToolbarButtonPanel({
     headerTitle: expectedLabel,
-    headerDescription: "",
+    headerDescription: expectedDescriptionLabel,
     enabledItems: [
       "PanelUI-fxa-cta-menu",
-      "PanelUI-fxa-menu-sync-button",
       "PanelUI-fxa-menu-monitor-button",
       "PanelUI-fxa-menu-relay-button",
       "PanelUI-fxa-menu-vpn-button",
@@ -690,7 +693,6 @@ add_task(async function test_experiment_ui_state_signedin() {
       "PanelUI-fxa-menu-sync-prefs-button",
       "PanelUI-fxa-menu-account-signout-button",
       "PanelUI-fxa-cta-menu",
-      "PanelUI-fxa-menu-sync-button",
       "PanelUI-fxa-menu-monitor-button",
       "PanelUI-fxa-menu-relay-button",
       "PanelUI-fxa-menu-vpn-button",
diff --git a/browser/base/content/test/tabPrompts/browser.toml b/browser/base/content/test/tabPrompts/browser.toml
index 037f1f0d2b..aa7d4c724e 100644
--- a/browser/base/content/test/tabPrompts/browser.toml
+++ b/browser/base/content/test/tabPrompts/browser.toml
@@ -39,6 +39,8 @@ support-files = ["file_beforeunload_stop.html"]
 https_first_disabled = true
 support-files = ["openPromptOffTimeout.html"]
 
+["browser_promptDelays.js"]
+
 ["browser_promptFocus.js"]
 
 ["browser_prompt_close_event.js"]
diff --git a/browser/base/content/test/tabPrompts/browser_promptDelays.js b/browser/base/content/test/tabPrompts/browser_promptDelays.js
new file mode 100644
index 0000000000..ecd01cdb69
--- /dev/null
+++ b/browser/base/content/test/tabPrompts/browser_promptDelays.js
@@ -0,0 +1,113 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const PERMISSION_DIALOG =
+  "chrome://mozapps/content/handling/permissionDialog.xhtml";
+
+add_setup(async function () {
+  // Set a new handler as default.
+  const protoSvc = Cc[
+    "@mozilla.org/uriloader/external-protocol-service;1"
+  ].getService(Ci.nsIExternalProtocolService);
+  let protoInfo = protoSvc.getProtocolHandlerInfo("web+testprotocol");
+  protoInfo.preferredAction = protoInfo.useHelperApp;
+  let handler = Cc["@mozilla.org/uriloader/web-handler-app;1"].createInstance(
+    Ci.nsIWebHandlerApp
+  );
+  handler.uriTemplate = "https://example.com/foobar?uri=%s";
+  handler.name = "Test protocol";
+  let handlers = protoInfo.possibleApplicationHandlers;
+  handlers.appendElement(handler);
+
+  protoInfo.preferredApplicationHandler = handler;
+  protoInfo.alwaysAskBeforeHandling = false;
+
+  const handlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  handlerSvc.store(protoInfo);
+
+  registerCleanupFunction(() => {
+    handlerSvc.remove(protoInfo);
+  });
+});
+
+add_task(async function test_promptWhileNotForeground() {
+  await BrowserTestUtils.withNewTab("about:blank", async browser => {
+    let windowOpened = BrowserTestUtils.waitForNewWindow();
+    await SpecialPowers.spawn(browser, [], () => {
+      content.eval(`window.open('about:blank', "_blank", "height=600");`);
+    });
+    let otherWin = await windowOpened;
+    info("Opened extra window, now start a prompt.");
+
+    // To ensure we test the delay helper correctly, shorten the delay:
+    await SpecialPowers.pushPrefEnv({
+      set: [["security.dialog_enable_delay", 50]],
+    });
+
+    let promptPromise = BrowserTestUtils.promiseAlertDialogOpen(
+      null,
+      PERMISSION_DIALOG,
+      { isSubDialog: true }
+    );
+    await SpecialPowers.spawn(browser, [], () => {
+      content.document.location.href = "web+testprotocol:hello";
+    });
+    info("Started opening prompt.");
+    let prompt = await promptPromise;
+    info("Opened prompt.");
+    let dialog = prompt.document.querySelector("dialog");
+    let button = dialog.getButton("accept");
+    is(button.getAttribute("disabled"), "true", "Button should be disabled");
+
+    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+    await new Promise(r => setTimeout(r, 500));
+    is(
+      button.getAttribute("disabled"),
+      "true",
+      "Button should still be disabled while the dialog is in the background"
+    );
+
+    let buttonGetsEnabled = BrowserTestUtils.waitForMutationCondition(
+      button,
+      { attributeFilter: ["disabled"] },
+      () => button.getAttribute("disabled") != "true"
+    );
+    await BrowserTestUtils.closeWindow(otherWin);
+    info("Waiting for button to be enabled.");
+    await buttonGetsEnabled;
+    ok(true, "The button was enabled.");
+    dialog.cancelDialog();
+
+    await SpecialPowers.popPrefEnv();
+  });
+});
+
+add_task(async function test_promptWhileForeground() {
+  await BrowserTestUtils.withNewTab("about:blank", async browser => {
+    let promptPromise = BrowserTestUtils.promiseAlertDialogOpen(
+      null,
+      PERMISSION_DIALOG,
+      { isSubDialog: true }
+    );
+    await SpecialPowers.spawn(browser, [], () => {
+      content.document.location.href = "web+testprotocol:hello";
+    });
+    info("Started opening prompt.");
+    let prompt = await promptPromise;
+    info("Opened prompt.");
+    let dialog = prompt.document.querySelector("dialog");
+    let button = dialog.getButton("accept");
+    is(button.getAttribute("disabled"), "true", "Button should be disabled");
+    await BrowserTestUtils.waitForMutationCondition(
+      button,
+      { attributeFilter: ["disabled"] },
+      () => button.getAttribute("disabled") != "true"
+    );
+    ok(true, "The button was enabled.");
+    dialog.cancelDialog();
+  });
+});
diff --git a/browser/base/content/test/tabPrompts/browser_promptFocus.js b/browser/base/content/test/tabPrompts/browser_promptFocus.js
index 89ca064c10..cab812f57b 100644
--- a/browser/base/content/test/tabPrompts/browser_promptFocus.js
+++ b/browser/base/content/test/tabPrompts/browser_promptFocus.js
@@ -20,8 +20,7 @@ add_task(async function test_tabdialogbox_tab_switch_focus() {
     tabPromises.push(
       BrowserTestUtils.openNewForegroundTab(
         gBrowser,
-        // eslint-disable-next-line @microsoft/sdl/no-insecure-url
-        "http://example.com",
+        "https://example.com",
         true
       )
     );
diff --git a/browser/base/content/test/tabs/browser.toml b/browser/base/content/test/tabs/browser.toml
index fa77a8b1a4..8a95c87a6e 100644
--- a/browser/base/content/test/tabs/browser.toml
+++ b/browser/base/content/test/tabs/browser.toml
@@ -30,6 +30,8 @@ skip-if = [
 ["browser_bfcache_exemption_about_pages.js"]
 skip-if = ["!fission"]
 
+["browser_blank_tab_label.js"]
+
 ["browser_bug580956.js"]
 
 ["browser_bug_1387976_restore_lazy_tab_browser_muted_state.js"]
@@ -140,6 +142,8 @@ support-files = [
 
 ["browser_multiselect_tabs_close.js"]
 
+["browser_multiselect_tabs_close_duplicate_tabs.js"]
+
 ["browser_multiselect_tabs_close_other_tabs.js"]
 
 ["browser_multiselect_tabs_close_tabs_to_the_left.js"]
diff --git a/browser/base/content/test/tabs/browser_blank_tab_label.js b/browser/base/content/test/tabs/browser_blank_tab_label.js
new file mode 100644
index 0000000000..9fe5f6b1b0
--- /dev/null
+++ b/browser/base/content/test/tabs/browser_blank_tab_label.js
@@ -0,0 +1,49 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Ensure that we don't use an entirely-blank (non-printable) document title
+ * as the tab label.
+ */
+add_task(async function test_ensure_printable_label() {
+  const TEST_DOC = `
+  <!DOCTYPE html>
+  <meta charset="utf-8">
+  <!-- Title is NO-BREAK SPACE, COMBINING ACUTE ACCENT, ARABIC LETTER MARK -->
+  <title>&nbsp;&%23x0301;&%23x061C;</title>
+  Is my title blank?`;
+
+  let newTab;
+  function tabLabelChecker() {
+    Assert.stringMatches(
+      newTab.label,
+      /\p{L}|\p{N}|\p{P}|\p{S}/u,
+      "Tab label should contain printable character."
+    );
+  }
+  let mutationObserver = new MutationObserver(tabLabelChecker);
+  registerCleanupFunction(() => mutationObserver.disconnect());
+
+  gBrowser.tabContainer.addEventListener(
+    "TabOpen",
+    event => {
+      newTab = event.target;
+      tabLabelChecker();
+      mutationObserver.observe(newTab, {
+        attributeFilter: ["label"],
+      });
+    },
+    { once: true }
+  );
+
+  await BrowserTestUtils.withNewTab("data:text/html," + TEST_DOC, async () => {
+    // Wait another longer-than-tick to ensure more mutation observer things have
+    // come in.
+    await new Promise(executeSoon);
+
+    // Check one last time for good measure, for the final label:
+    tabLabelChecker();
+  });
+});
diff --git a/browser/base/content/test/tabs/browser_multiselect_tabs_close_duplicate_tabs.js b/browser/base/content/test/tabs/browser_multiselect_tabs_close_duplicate_tabs.js
new file mode 100644
index 0000000000..d18795447f
--- /dev/null
+++ b/browser/base/content/test/tabs/browser_multiselect_tabs_close_duplicate_tabs.js
@@ -0,0 +1,178 @@
+const PREF_WARN_ON_CLOSE = "browser.tabs.warnOnCloseOtherTabs";
+const PREF_SHOWN_DUPE_DIALOG =
+  "browser.tabs.haveShownCloseAllDuplicateTabsWarning";
+
+add_task(async function setPref() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      [PREF_WARN_ON_CLOSE, false],
+      [PREF_SHOWN_DUPE_DIALOG, true],
+    ],
+  });
+});
+
+add_task(async function withAMultiSelectedTab() {
+  let initialTab = gBrowser.selectedTab;
+  let tab1 = await addTab();
+  let tab2 = await addTab();
+  let tab3 = await addTab();
+  let tab4 = await addTab();
+
+  is(gBrowser.multiSelectedTabsCount, 0, "Zero multiselected tabs");
+
+  await triggerClickOn(tab1, { ctrlKey: true });
+
+  let tab4Pinned = BrowserTestUtils.waitForEvent(tab4, "TabPinned");
+  gBrowser.pinTab(tab4);
+  await tab4Pinned;
+
+  ok(initialTab.multiselected, "InitialTab is multiselected");
+  ok(tab1.multiselected, "Tab1 is multiselected");
+  ok(!tab2.multiselected, "Tab2 is not multiselected");
+  ok(!tab3.multiselected, "Tab3 is not multiselected");
+  ok(!tab4.multiselected, "Tab4 is not multiselected");
+  ok(tab4.pinned, "Tab4 is pinned");
+  is(gBrowser.multiSelectedTabsCount, 2, "Two multiselected tabs");
+  is(gBrowser.selectedTab, initialTab, "InitialTab is the active tab");
+
+  let closingTabs = [tab2, tab3];
+  let tabClosingPromises = [];
+  for (let tab of closingTabs) {
+    tabClosingPromises.push(BrowserTestUtils.waitForTabClosing(tab));
+  }
+
+  gBrowser.removeDuplicateTabs(tab1);
+
+  await Promise.all(tabClosingPromises);
+
+  ok(!initialTab.closing, "InitialTab is not closing");
+  ok(!tab1.closing, "Tab1 is not closing");
+  ok(tab2.closing, "Tab2 is closing");
+  ok(tab3.closing, "Tab3 is closing");
+  ok(!tab4.closing, "Tab4 is not closing");
+  is(gBrowser.multiSelectedTabsCount, 2, "Two multiselected tabs");
+  is(gBrowser.selectedTab, initialTab, "InitialTab is still the active tab");
+
+  gBrowser.clearMultiSelectedTabs();
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab4);
+});
+
+add_task(async function withNotAMultiSelectedTab() {
+  let initialTab = gBrowser.selectedTab;
+  let tab1 = await addTab("http://mochi.test:8888/");
+  let tab2 = await addTab("http://mochi.test:8888/");
+  let tab3 = await addTab("http://mochi.test:8888/");
+  let tab4 = await addTab("http://mochi.test:8888/");
+  let tab5 = await addTab("http://mochi.test:8888/");
+  let tab6 = await addTab("http://mochi.test:8888/", { userContextId: 1 });
+
+  is(gBrowser.multiSelectedTabsCount, 0, "Zero multiselected tabs");
+
+  await BrowserTestUtils.switchTab(gBrowser, tab1);
+  await triggerClickOn(tab2, { ctrlKey: true });
+  await triggerClickOn(tab5, { ctrlKey: true });
+
+  let tab4Pinned = BrowserTestUtils.waitForEvent(tab4, "TabPinned");
+  gBrowser.pinTab(tab4);
+  await tab4Pinned;
+
+  let tab5Pinned = BrowserTestUtils.waitForEvent(tab5, "TabPinned");
+  gBrowser.pinTab(tab5);
+  await tab5Pinned;
+
+  ok(!initialTab.multiselected, "InitialTab is not multiselected");
+  ok(tab1.multiselected, "Tab1 is multiselected");
+  ok(tab2.multiselected, "Tab2 is multiselected");
+  ok(!tab3.multiselected, "Tab3 is not multiselected");
+  ok(!tab4.multiselected, "Tab4 is not multiselected");
+  ok(tab4.pinned, "Tab4 is pinned");
+  ok(tab5.multiselected, "Tab5 is multiselected");
+  ok(tab5.pinned, "Tab5 is pinned");
+  ok(!tab6.multiselected, "Tab6 is not multiselected");
+  ok(!tab6.pinned, "Tab6 is not pinned");
+  is(gBrowser.multiSelectedTabsCount, 3, "Three multiselected tabs");
+  is(gBrowser.selectedTab, tab1, "Tab1 is the active tab");
+
+  let closingTabs = [tab1, tab2];
+  let tabClosingPromises = [];
+  for (let tab of closingTabs) {
+    tabClosingPromises.push(BrowserTestUtils.waitForTabClosing(tab));
+  }
+
+  await BrowserTestUtils.switchTab(
+    gBrowser,
+    gBrowser.removeDuplicateTabs(tab3)
+  );
+
+  await Promise.all(tabClosingPromises);
+
+  ok(!initialTab.closing, "InitialTab is not closing");
+  ok(tab1.closing, "Tab1 is closing");
+  ok(tab2.closing, "Tab2 is closing");
+  ok(!tab3.closing, "Tab3 is not closing");
+  ok(!tab4.closing, "Tab4 is not closing");
+  ok(!tab5.closing, "Tab5 is not closing");
+  ok(!tab6.closing, "Tab6 is not closing");
+  is(
+    gBrowser.multiSelectedTabsCount,
+    0,
+    "Zero multiselected tabs, selection is cleared"
+  );
+  is(gBrowser.selectedTab, tab3, "tab3 is the active tab now");
+
+  for (let tab of [tab3, tab4, tab5, tab6]) {
+    BrowserTestUtils.removeTab(tab);
+  }
+});
+
+add_task(async function closeAllDuplicateTabs() {
+  let initialTab = gBrowser.selectedTab;
+  let tab1 = await addTab("http://mochi.test:8888/one");
+  let tab2 = await addTab("http://mochi.test:8888/two", { userContextId: 1 });
+  let tab3 = await addTab("http://mochi.test:8888/one");
+  let tab4 = await addTab("http://mochi.test:8888/two");
+  let tab5 = await addTab("http://mochi.test:8888/one");
+  let tab6 = await addTab("http://mochi.test:8888/two");
+
+  let tab1Pinned = BrowserTestUtils.waitForEvent(tab1, "TabPinned");
+  gBrowser.pinTab(tab1);
+  await tab1Pinned;
+
+  // So we have 1p,2c,1,2,1,2
+  // We expect 1p,2c,X,2,X,X because the pinned 1 will dupe the other two 1,
+  // but the 2c's userContextId makes it unique against the other two 2,
+  // but one of the other two 2 will close.
+
+  // Ensure tab4 remains by making it active more recently than tab6.
+  tab4._lastSeenActive = Date.now(); // as recent as it gets.
+
+  // Assert some preconditions:
+  ok(tab1.pinned, "Tab1 is pinned");
+  Assert.greater(tab4.lastSeenActive, tab6.lastSeenActive);
+
+  let closingTabs = [tab3, tab5, tab6];
+  let tabClosingPromises = [];
+  for (let tab of closingTabs) {
+    tabClosingPromises.push(BrowserTestUtils.waitForTabClosing(tab));
+  }
+
+  await BrowserTestUtils.switchTab(
+    gBrowser,
+    gBrowser.removeAllDuplicateTabs(initialTab)
+  );
+
+  await Promise.all(tabClosingPromises);
+
+  ok(!initialTab.closing, "InitialTab is not closing");
+  ok(!tab1.closing, "Tab1 is not closing");
+  ok(!tab2.closing, "Tab2 is not closing");
+  ok(tab3.closing, "Tab3 is closing");
+  ok(!tab4.closing, "Tab4 is not closing");
+  ok(tab5.closing, "Tab5 is closing");
+  ok(tab6.closing, "Tab6 is closing");
+
+  for (let tab of [tab1, tab2, tab4]) {
+    BrowserTestUtils.removeTab(tab);
+  }
+});
diff --git a/browser/base/content/test/tabs/browser_tab_preview.js b/browser/base/content/test/tabs/browser_tab_preview.js
index 0f83b1e28c..19ba85b9f8 100644
--- a/browser/base/content/test/tabs/browser_tab_preview.js
+++ b/browser/base/content/test/tabs/browser_tab_preview.js
@@ -34,6 +34,7 @@ add_setup(async function () {
     set: [
       ["browser.tabs.cardPreview.enabled", true],
       ["browser.tabs.cardPreview.showThumbnails", false],
+      ["browser.tabs.tooltipsShowPidAndActiveness", false],
       ["ui.tooltip.delay_ms", 0],
     ],
   });
@@ -82,6 +83,99 @@ add_task(async function hoverTests() {
 });
 
 /**
+ * Verify that the pid and activeness statuses are not shown
+ * when the flag is not enabled.
+ */
+add_task(async function pidAndActivenessHiddenByDefaultTests() {
+  const tabUrl1 =
+    "data:text/html,<html><head><title>First New Tab</title></head><body>Hello</body></html>";
+  const tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, tabUrl1);
+  const previewContainer = document.getElementById("tab-preview-panel");
+
+  await openPreview(tab1);
+  Assert.equal(
+    previewContainer.querySelector(".tab-preview-pid").innerText,
+    "",
+    "Tab PID is not shown"
+  );
+  Assert.equal(
+    previewContainer.querySelector(".tab-preview-activeness").innerText,
+    "",
+    "Tab activeness is not shown"
+  );
+
+  await closePreviews();
+
+  BrowserTestUtils.removeTab(tab1);
+
+  // Move the mouse outside of the tab strip.
+  EventUtils.synthesizeMouseAtCenter(document.documentElement, {
+    type: "mouseover",
+  });
+});
+
+add_task(async function pidAndActivenessTests() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.tabs.tooltipsShowPidAndActiveness", true]],
+  });
+
+  const tabUrl1 =
+    "data:text/html,<html><head><title>Single process tab</title></head><body>Hello</body></html>";
+  const tab1 = await BrowserTestUtils.openNewForegroundTab(gBrowser, tabUrl1);
+  const tabUrl2 = `data:text/html,<html>
+      <head>
+        <title>Multi-process tab</title>
+      </head>
+      <body>
+        <iframe
+          id="inlineFrameExample"
+          title="Inline Frame Example"
+          width="300"
+          height="200"
+          src="https://example.com">
+        </iframe>
+      </body>
+    </html>`;
+  const tab2 = await BrowserTestUtils.openNewForegroundTab(gBrowser, tabUrl2);
+  const previewContainer = document.getElementById("tab-preview-panel");
+
+  await openPreview(tab1);
+  Assert.stringMatches(
+    previewContainer.querySelector(".tab-preview-pid").innerText,
+    /^pid: \d+$/,
+    "Tab PID is shown on single process tab"
+  );
+  Assert.equal(
+    previewContainer.querySelector(".tab-preview-activeness").innerText,
+    "",
+    "Tab activeness is not shown on inactive tab"
+  );
+  await closePreviews();
+
+  await openPreview(tab2);
+  Assert.stringMatches(
+    previewContainer.querySelector(".tab-preview-pid").innerText,
+    /^pids: \d+, \d+$/,
+    "Tab PIDs are shown on multi-process tab"
+  );
+  Assert.equal(
+    previewContainer.querySelector(".tab-preview-activeness").innerText,
+    "[A]",
+    "Tab activeness is shown on active tab"
+  );
+  await closePreviews();
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+  await SpecialPowers.popPrefEnv();
+
+  // Move the mouse outside of the tab strip.
+  EventUtils.synthesizeMouseAtCenter(document.documentElement, {
+    type: "mouseover",
+  });
+});
+
+/**
  * Verify that non-selected tabs display a thumbnail in their preview
  * when browser.tabs.cardPreview.showThumbnails is set to true,
  * while the currently selected tab never displays a thumbnail in its preview.
diff --git a/browser/base/content/test/tabs/browser_visibleTabs_contextMenu.js b/browser/base/content/test/tabs/browser_visibleTabs_contextMenu.js
index 202c43ce47..06fdd27d9c 100644
--- a/browser/base/content/test/tabs/browser_visibleTabs_contextMenu.js
+++ b/browser/base/content/test/tabs/browser_visibleTabs_contextMenu.js
@@ -2,11 +2,6 @@
  * 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/. */
 
-const remoteClientsFixture = [
-  { id: 1, name: "Foo" },
-  { id: 2, name: "Bar" },
-];
-
 add_task(async function test() {
   // There should be one tab when we start the test
   let [origTab] = gBrowser.visibleTabs;
@@ -16,9 +11,8 @@ add_task(async function test() {
 
   // Check the context menu with two tabs
   updateTabContextMenu(origTab);
-  is(
-    document.getElementById("context_closeTab").disabled,
-    false,
+  ok(
+    !document.getElementById("context_closeTab").disabled,
     "Close Tab is enabled"
   );
 
@@ -29,11 +23,14 @@ add_task(async function test() {
 
   // Check the context menu with one tab.
   updateTabContextMenu(testTab);
-  is(
-    document.getElementById("context_closeTab").disabled,
-    false,
+  ok(
+    !document.getElementById("context_closeTab").disabled,
     "Close Tab is enabled when more than one tab exists"
   );
+  ok(
+    !document.getElementById("context_closeDuplicateTabs").disabled,
+    "Close duplicate tabs is enabled when more than one tab with the same URL exists"
+  );
 
   // Add a tab that will get pinned
   // So now there's one pinned tab, one visible unpinned tab, and one hidden tab
diff --git a/browser/base/content/test/webextensions/browser_aboutaddons_blanktab.js b/browser/base/content/test/webextensions/browser_aboutaddons_blanktab.js
index 228fe71815..1e0814ea96 100644
--- a/browser/base/content/test/webextensions/browser_aboutaddons_blanktab.js
+++ b/browser/base/content/test/webextensions/browser_aboutaddons_blanktab.js
@@ -8,7 +8,7 @@ add_task(async function testBlankTabReusedAboutAddons() {
     is(browser, gBrowser.selectedBrowser, "New tab is selected");
 
     // Opening about:addons shouldn't change the selected tab.
-    BrowserOpenAddonsMgr();
+    BrowserAddonUI.openAddonsMgr();
 
     is(browser, gBrowser.selectedBrowser, "No new tab was opened");
 
diff --git a/browser/base/content/test/webextensions/browser_extension_sideloading.js b/browser/base/content/test/webextensions/browser_extension_sideloading.js
index 4e1fe07194..5d8f82a178 100644
--- a/browser/base/content/test/webextensions/browser_extension_sideloading.js
+++ b/browser/base/content/test/webextensions/browser_extension_sideloading.js
@@ -16,11 +16,14 @@ const kSideloaded = true;
 async function createWebExtension(details) {
   let options = {
     manifest: {
+      manifest_version: details.manifest_version ?? 2,
+
       browser_specific_settings: { gecko: { id: details.id } },
 
       name: details.name,
 
       permissions: details.permissions,
+      host_permissions: details.host_permissions,
     },
   };
 
@@ -86,9 +89,10 @@ add_task(async function test_sideloading() {
 
   const ID2 = "addon2@tests.mozilla.org";
   await createWebExtension({
+    manifest_version: 3,
     id: ID2,
     name: "Test 2",
-    permissions: ["<all_urls>"],
+    host_permissions: ["<all_urls>"],
   });
 
   const ID3 = "addon3@tests.mozilla.org";
@@ -224,7 +228,7 @@ add_task(async function test_sideloading() {
   // Close the hamburger menu and go directly to the addons manager
   await gCUITestUtils.hideMainMenu();
 
-  win = await BrowserOpenAddonsMgr(VIEW);
+  win = await BrowserAddonUI.openAddonsMgr(VIEW);
   await waitAboutAddonsViewLoaded(win.document);
 
   // about:addons addon entry element.
@@ -293,7 +297,7 @@ add_task(async function test_sideloading() {
   // Close the hamburger menu and go to the detail page for this addon
   await gCUITestUtils.hideMainMenu();
 
-  win = await BrowserOpenAddonsMgr(
+  win = await BrowserAddonUI.openAddonsMgr(
     `addons://detail/${encodeURIComponent(ID3)}`
   );
 
diff --git a/browser/base/content/test/webextensions/browser_permissions_local_file.js b/browser/base/content/test/webextensions/browser_permissions_local_file.js
index 22dff8cb38..731e8adea7 100644
--- a/browser/base/content/test/webextensions/browser_permissions_local_file.js
+++ b/browser/base/content/test/webextensions/browser_permissions_local_file.js
@@ -14,7 +14,9 @@ async function installFile(filename) {
   MockFilePicker.setFiles([file]);
   MockFilePicker.afterOpenCallback = MockFilePicker.cleanup;
 
-  let { document } = await BrowserOpenAddonsMgr("addons://list/extension");
+  let { document } = await BrowserAddonUI.openAddonsMgr(
+    "addons://list/extension"
+  );
 
   // Do the install...
   await waitAboutAddonsViewLoaded(document);
diff --git a/browser/base/content/test/webextensions/browser_update_interactive_noprompt.js b/browser/base/content/test/webextensions/browser_update_interactive_noprompt.js
index 0b0b912503..9ad3deaae1 100644
--- a/browser/base/content/test/webextensions/browser_update_interactive_noprompt.js
+++ b/browser/base/content/test/webextensions/browser_update_interactive_noprompt.js
@@ -36,7 +36,7 @@ async function testUpdateNoPrompt(
   is(addon.version, initialVersion, "Version 1 of the addon is installed");
 
   // Go to Extensions in about:addons
-  let win = await BrowserOpenAddonsMgr("addons://list/extension");
+  let win = await BrowserAddonUI.openAddonsMgr("addons://list/extension");
 
   await waitAboutAddonsViewLoaded(win.document);
 
diff --git a/browser/base/content/test/webextensions/head.js b/browser/base/content/test/webextensions/head.js
index f1183c61b8..f364dbed88 100644
--- a/browser/base/content/test/webextensions/head.js
+++ b/browser/base/content/test/webextensions/head.js
@@ -508,7 +508,7 @@ async function interactiveUpdateTest(autoUpdate, checkFn) {
   ok(addon, "Addon was installed");
   is(addon.version, "1.0", "Version 1 of the addon is installed");
 
-  let win = await BrowserOpenAddonsMgr("addons://list/extension");
+  let win = await BrowserAddonUI.openAddonsMgr("addons://list/extension");
 
   await waitAboutAddonsViewLoaded(win.document);
 
diff --git a/browser/base/content/utilityOverlay.js b/browser/base/content/utilityOverlay.js
index dc3aeffaed..1d8637db2e 100644
--- a/browser/base/content/utilityOverlay.js
+++ b/browser/base/content/utilityOverlay.js
@@ -113,11 +113,6 @@ function getRootEvent(aEvent) {
   return BrowserUtils.getRootEvent(aEvent);
 }
 
-// This is here for historical reasons. bug 1742889 covers cleaning this up.
-function whereToOpenLink(e, ignoreButton, ignoreAlt) {
-  return BrowserUtils.whereToOpenLink(e, ignoreButton, ignoreAlt);
-}
-
 function openTrustedLinkIn(url, where, params) {
   URILoadingHelper.openTrustedLinkIn(window, url, where, params);
 }