--- a/browser/components/customizableui/test/browser.ini
+++ b/browser/components/customizableui/test/browser.ini
@@ -94,17 +94,16 @@ skip-if = os == "linux" # Intermittent f
 [browser_947987_removable_default.js]
 [browser_948985_non_removable_defaultArea.js]
 [browser_952963_areaType_getter_no_area.js]
 [browser_956602_remove_special_widget.js]
 [browser_962069_drag_to_overflow_chevron.js]
 [browser_962884_opt_in_disable_hyphens.js]
 [browser_963639_customizing_attribute_non_customizable_toolbar.js]
 [browser_967000_button_charEncoding.js]
-skip-if = e10s # Bug 1088710
 [browser_967000_button_feeds.js]
 [browser_967000_button_sync.js]
 [browser_968447_bookmarks_toolbar_items_in_panel.js]
 skip-if = os == "linux" # Intemittent failures - bug 979207
 [browser_968565_insert_before_hidden_items.js]
 [browser_969427_recreate_destroyed_widget_after_reset.js]
 [browser_969661_character_encoding_navbar_disabled.js]
 [browser_970511_undo_restore_default.js]
@@ -122,17 +121,16 @@ skip-if = os == "linux"
 [browser_984455_bookmarks_items_reparenting.js]
 skip-if = os == "linux"
 [browser_985815_propagate_setToolbarVisibility.js]
 [browser_987177_destroyWidget_xul.js]
 [browser_987177_xul_wrapper_updating.js]
 [browser_987185_syncButton.js]
 [browser_987492_window_api.js]
 [browser_987640_charEncoding.js]
-skip-if = e10s # Bug 1088710
 [browser_988072_sidebar_events.js]
 [browser_989338_saved_placements_not_resaved.js]
 [browser_989751_subviewbutton_class.js]
 [browser_992747_toggle_noncustomizable_toolbar.js]
 [browser_993322_widget_notoolbar.js]
 [browser_995164_registerArea_during_customize_mode.js]
 [browser_996364_registerArea_different_properties.js]
 [browser_996635_remove_non_widgets.js]

--- a/browser/components/customizableui/test/browser_967000_button_charEncoding.js
+++ b/browser/components/customizableui/test/browser_967000_button_charEncoding.js
@@ -1,19 +1,16 @@
 /* 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/. */
 
 "use strict";
 
 const TEST_PAGE = "http://mochi.test:8888/browser/browser/components/customizableui/test/support/test_967000_charEncoding_page.html";
 
-var newTab;
-var initialLocation = gBrowser.currentURI.spec;
-
 add_task(function*() {
   info("Check Character Encoding button functionality");
 
   // add the Character Encoding button to the panel
   CustomizableUI.addWidgetToArea("characterencoding-button",
                                   CustomizableUI.AREA_PANEL);
 
   // check the button's functionality
@@ -23,24 +20,25 @@ add_task(function*() {
   ok(charEncodingButton, "The Character Encoding button was added to the Panel Menu");
   is(charEncodingButton.getAttribute("disabled"), "true",
      "The Character encoding button is initially disabled");
 
   let panelHidePromise = promisePanelHidden(window);
   PanelUI.hide();
   yield panelHidePromise;
 
-  newTab = gBrowser.selectedTab;
-  yield promiseTabLoadEvent(newTab, TEST_PAGE)
+  let newTab = yield BrowserTestUtils.openNewForegroundTab(gBrowser, TEST_PAGE, true);
 
   yield PanelUI.show();
   ok(!charEncodingButton.hasAttribute("disabled"), "The Character encoding button gets enabled");
+  let characterEncodingView = document.getElementById("PanelUI-characterEncodingView");
+  let subviewShownPromise = subviewShown(characterEncodingView);
   charEncodingButton.click();
+  yield subviewShownPromise;
 
-  let characterEncodingView = document.getElementById("PanelUI-characterEncodingView");
   ok(characterEncodingView.hasAttribute("current"), "The Character encoding panel is displayed");
 
   let pinnedEncodings = document.getElementById("PanelUI-characterEncodingView-pinned");
   let charsetsList = document.getElementById("PanelUI-characterEncodingView-charsets");
   ok(pinnedEncodings, "Pinned charsets are available");
   ok(charsetsList, "Charsets list is available");
 
   let checkedButtons = characterEncodingView.querySelectorAll("toolbarbutton[checked='true']");
@@ -48,19 +46,17 @@ add_task(function*() {
   is(checkedButtons[0].getAttribute("label"), "Unicode", "The unicode encoding is correctly selected");
   is(characterEncodingView.querySelectorAll("#PanelUI-characterEncodingView-autodetect toolbarbutton[checked='true']").length,
      1,
      "There should be 1 checked detector.");
 
   panelHidePromise = promisePanelHidden(window);
   PanelUI.hide();
   yield panelHidePromise;
+
+  yield BrowserTestUtils.removeTab(newTab);
 });
 
 add_task(function* asyncCleanup() {
   // reset the panel to the default state
   yield resetCustomization();
   ok(CustomizableUI.inDefaultState, "The UI is in default state again.");
-
-  // restore the initial location
-  gBrowser.addTab(initialLocation);
-  gBrowser.removeTab(newTab);
 });

--- a/browser/components/customizableui/test/browser_987640_charEncoding.js
+++ b/browser/components/customizableui/test/browser_987640_charEncoding.js
@@ -1,32 +1,32 @@
 /* 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/. */
 
 "use strict";
 
 const TEST_PAGE = "http://mochi.test:8888/browser/browser/components/customizableui/test/support/test_967000_charEncoding_page.html";
-var newTab = null;
 
 add_task(function*() {
   info("Check Character Encoding panel functionality");
 
   // add the Character Encoding button to the panel
   CustomizableUI.addWidgetToArea("characterencoding-button",
                                   CustomizableUI.AREA_PANEL);
 
-  newTab = gBrowser.addTab(TEST_PAGE);
-  yield promiseTabLoadEvent(gBrowser.selectedTab, TEST_PAGE);
+  let newTab = yield BrowserTestUtils.openNewForegroundTab(gBrowser, TEST_PAGE, true);
 
   yield PanelUI.show();
   let charEncodingButton = document.getElementById("characterencoding-button");
+  let characterEncodingView = document.getElementById("PanelUI-characterEncodingView");
+  let subviewShownPromise = subviewShown(characterEncodingView);
   charEncodingButton.click();
+  yield subviewShownPromise;
 
-  let characterEncodingView = document.getElementById("PanelUI-characterEncodingView");
   let checkedButtons = characterEncodingView.querySelectorAll("toolbarbutton[checked='true']");
   let initialEncoding = checkedButtons[0];
   is(initialEncoding.getAttribute("label"), "Unicode", "The unicode encoding is initially selected");
 
   // change the encoding
   let encodings = characterEncodingView.querySelectorAll("toolbarbutton");
   let newEncoding = encodings[0].hasAttribute("checked") ? encodings[1] : encodings[0];
   let tabLoadPromise = promiseTabLoadEvent(gBrowser.selectedTab, TEST_PAGE);
@@ -45,18 +45,16 @@ add_task(function*() {
   charEncodingButton.click();
   tabLoadPromise = promiseTabLoadEvent(gBrowser.selectedTab, TEST_PAGE);
   initialEncoding.click();
   yield tabLoadPromise;
   yield PanelUI.show();
   charEncodingButton.click();
   checkedButtons = characterEncodingView.querySelectorAll("toolbarbutton[checked='true']");
   is(checkedButtons[0].getAttribute("label"), "Unicode", "The encoding was reset to Unicode");
+  yield BrowserTestUtils.removeTab(newTab);
 });
 
 add_task(function* asyncCleanup() {
   // reset the panel to the default state
   yield resetCustomization();
   ok(CustomizableUI.inDefaultState, "The UI is in default state again.");
-
-  // remove the added tab
-  gBrowser.removeTab(newTab);
 });

--- a/toolkit/content/browser-child.js
+++ b/toolkit/content/browser-child.js
@@ -123,16 +123,18 @@ var WebProgressListener = {
     json.status = aStatus;
 
     // It's possible that this state change was triggered by
     // loading an internal error page, for which the parent
     // will want to know some details, so we'll update it with
     // the documentURI.
     if (aWebProgress && aWebProgress.isTopLevel) {
       json.documentURI = content.document.documentURIObject.spec;
+      json.charset = content.document.characterSet;
+      json.mayEnableCharacterEncodingMenu = docShell.mayEnableCharacterEncodingMenu;
     }
 
     this._send("Content:StateChange", json, objects);
   },
 
   onProgressChange: function onProgressChange(aWebProgress, aRequest, aCurSelf, aMaxSelf, aCurTotal, aMaxTotal) {
     let json = this._setupJSON(aWebProgress, aRequest);
     let objects = this._setupObjects(aWebProgress, aRequest);

--- a/toolkit/modules/RemoteWebProgress.jsm
+++ b/toolkit/modules/RemoteWebProgress.jsm
@@ -206,16 +206,20 @@ RemoteWebProgressManager.prototype = {
       request = new RemoteWebProgressRequest(json.requestURI,
                                              json.originalRequestURI,
                                              objects.request);
     }
 
     if (isTopLevel) {
       this._browser._contentWindow = objects.contentWindow;
       this._browser._documentContentType = json.documentContentType;
+      if (json.charset) {
+        this._browser._characterSet = json.charset;
+        this._browser._mayEnableCharacterEncodingMenu = json.mayEnableCharacterEncodingMenu;
+      }
     }
 
     switch (aMessage.name) {
     case "Content:StateChange":
       if (isTopLevel) {
         this._browser._documentURI = newURI(json.documentURI);
       }
       this._callProgressListeners("onStateChange", webProgress, request, json.stateFlags, json.status);
@@ -227,21 +231,19 @@ RemoteWebProgressManager.prototype = {
       let remoteWebNav = this._browser._remoteWebNavigationImpl;
 
       // These properties can change even for a sub-frame navigation.
       remoteWebNav.canGoBack = json.canGoBack;
       remoteWebNav.canGoForward = json.canGoForward;
 
       if (isTopLevel) {
         remoteWebNav._currentURI = location;
-        this._browser._characterSet = json.charset;
         this._browser._documentURI = newURI(json.documentURI);
         this._browser._contentTitle = json.title;
         this._browser._imageDocument = null;
-        this._browser._mayEnableCharacterEncodingMenu = json.mayEnableCharacterEncodingMenu;
         this._browser._contentPrincipal = json.principal;
         this._browser._isSyntheticDocument = json.synthetic;
         this._browser._innerWindowID = json.innerWindowID;
       }
 
       this._callProgressListeners("onLocationChange", webProgress, request, location, flags);
       break;