diff --git a/mobile/android/chrome/content/MemoryObserver.js b/mobile/android/chrome/content/MemoryObserver.js
index 5a90d43f06a5..54c14e151303 100644
--- a/mobile/android/chrome/content/MemoryObserver.js
+++ b/mobile/android/chrome/content/MemoryObserver.js
@@ -57,7 +57,7 @@ var MemoryObserver = {
   },
 
   gc: function() {
-    window.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils).garbageCollect();
+    window.windowUtils.garbageCollect();
     Cu.forceGC();
   },
 
diff --git a/mobile/android/chrome/content/PluginHelper.js b/mobile/android/chrome/content/PluginHelper.js
index 6e986b87d380..123ee5e6a88e 100644
--- a/mobile/android/chrome/content/PluginHelper.js
+++ b/mobile/android/chrome/content/PluginHelper.js
@@ -73,8 +73,7 @@ var PluginHelper = {
   },
 
   playAllPlugins: function(aContentWindow) {
-    let cwu = aContentWindow.QueryInterface(Ci.nsIInterfaceRequestor)
-                            .getInterface(Ci.nsIDOMWindowUtils);
+    let cwu = aContentWindow.windowUtils;
     // XXX not sure if we should enable plugins for the parent documents...
     let plugins = cwu.plugins;
     if (!plugins || !plugins.length)
diff --git a/mobile/android/chrome/content/browser.js b/mobile/android/chrome/content/browser.js
index 9edda1bb867e..001dc8a4b6be 100644
--- a/mobile/android/chrome/content/browser.js
+++ b/mobile/android/chrome/content/browser.js
@@ -1081,7 +1081,7 @@ var BrowserApp = {
   },
 
   contentDocumentChanged: function() {
-    window.top.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils).isFirstPaint = true;
+    window.top.windowUtils.isFirstPaint = true;
     Services.androidBridge.contentDocumentChanged(window);
   },
 
@@ -1650,8 +1650,7 @@ var BrowserApp = {
       return;
     }
 
-    let dwu = aBrowser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor)
-                                    .getInterface(Ci.nsIDOMWindowUtils);
+    let dwu = aBrowser.contentWindow.windowUtils;
     if (!dwu) {
       return;
     }
@@ -3824,7 +3823,7 @@ Tab.prototype = {
   reloadWithMode: function (aDesktopMode) {
     // notify desktopmode for PIDOMWindow
     let win = this.browser.contentWindow;
-    let dwi = win.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+    let dwi = win.windowUtils;
     dwi.setDesktopModeViewport(aDesktopMode);
 
     // Set desktop mode for tab and send change to Java
@@ -4781,7 +4780,7 @@ Tab.prototype = {
       case "audioFocusChanged":
       case "mediaControl":
         let win = this.browser.contentWindow;
-        let utils = win.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+        let utils = win.windowUtils;
         let suspendTypes = Ci.nsISuspendedTypes;
         switch (aData) {
           case "lostAudioFocus":
diff --git a/mobile/android/chrome/geckoview/GeckoViewContent.js b/mobile/android/chrome/geckoview/GeckoViewContent.js
index a1e65f34693c..33e86bd549eb 100644
--- a/mobile/android/chrome/geckoview/GeckoViewContent.js
+++ b/mobile/android/chrome/geckoview/GeckoViewContent.js
@@ -68,7 +68,7 @@ class GeckoViewContent extends GeckoViewContentModule {
 
     // Save the current document resolution.
     let zoom = { value: 1 };
-    let domWindowUtils = content.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+    let domWindowUtils = content.windowUtils;
     domWindowUtils.getResolution(zoom);
     scrolldata = scrolldata || {};
     scrolldata.zoom = {};
@@ -96,23 +96,20 @@ class GeckoViewContent extends GeckoViewContentModule {
     switch (aMsg.name) {
       case "GeckoView:DOMFullscreenEntered":
         if (content) {
-          content.QueryInterface(Ci.nsIInterfaceRequestor)
-                 .getInterface(Ci.nsIDOMWindowUtils)
+          content.windowUtils
                  .handleFullscreenRequests();
         }
         break;
 
       case "GeckoView:DOMFullscreenExited":
         if (content) {
-          content.QueryInterface(Ci.nsIInterfaceRequestor)
-                 .getInterface(Ci.nsIDOMWindowUtils)
+          content.windowUtils
                  .exitFullscreen();
         }
         break;
 
       case "GeckoView:ZoomToInput": {
-        let dwu = content.QueryInterface(Ci.nsIInterfaceRequestor)
-                         .getInterface(Ci.nsIDOMWindowUtils);
+        let dwu = content.windowUtils;
 
         let zoomToFocusedInput = function() {
           if (!dwu.flushApzRepaints()) {
@@ -294,7 +291,7 @@ class GeckoViewContent extends GeckoViewContentModule {
     if (this._savedState) {
       const scrolldata = this._savedState.scrolldata;
       if (scrolldata && scrolldata.zoom && scrolldata.zoom.displaySize) {
-        let utils = content.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+        let utils = content.windowUtils;
         // Restore zoom level.
         utils.setRestoreResolution(scrolldata.zoom.resolution,
                                    scrolldata.zoom.displaySize.width,
diff --git a/mobile/android/chrome/geckoview/GeckoViewContentSettings.js b/mobile/android/chrome/geckoview/GeckoViewContentSettings.js
index efa78f35a680..9ae3a4384726 100644
--- a/mobile/android/chrome/geckoview/GeckoViewContentSettings.js
+++ b/mobile/android/chrome/geckoview/GeckoViewContentSettings.js
@@ -43,8 +43,7 @@ class GeckoViewContentSettings extends GeckoViewContentModule {
     if (this.useDesktopMode === aUse) {
       return;
     }
-    let utils = content.QueryInterface(Ci.nsIInterfaceRequestor)
-                       .getInterface(Ci.nsIDOMWindowUtils);
+    let utils = content.windowUtils;
     utils.setDesktopModeViewport(aUse);
     this._useDesktopMode = aUse;
   }
diff --git a/mobile/android/components/ContentDispatchChooser.js b/mobile/android/components/ContentDispatchChooser.js
index 44df4db064d2..7b706424d3f1 100644
--- a/mobile/android/components/ContentDispatchChooser.js
+++ b/mobile/android/components/ContentDispatchChooser.js
@@ -83,7 +83,7 @@ ContentDispatchChooser.prototype =
         // We couldn't open this. If this was from a click, it's likely that we just
         // want this to fail silently. If the user entered this on the address bar, though,
         // we want to show the neterror page.
-        let dwu = window.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+        let dwu = window.windowUtils;
         let millis = dwu.millisSinceLastUserInput;
         if (millis < 0 || millis >= 1000) {
           window.document.docShell.displayLoadError(Cr.NS_ERROR_UNKNOWN_PROTOCOL, aURI, null);
diff --git a/mobile/android/components/FilePicker.js b/mobile/android/components/FilePicker.js
index a5c6cdfe971b..38adb0445b03 100644
--- a/mobile/android/components/FilePicker.js
+++ b/mobile/android/components/FilePicker.js
@@ -168,7 +168,7 @@ FilePicker.prototype = {
   show: function() {
     if (this._domWin) {
       this.fireDialogEvent(this._domWin, "DOMWillOpenModalDialog");
-      let winUtils = this._domWin.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+      let winUtils = this._domWin.windowUtils;
       winUtils.enterModalState();
     }
 
@@ -179,7 +179,7 @@ FilePicker.prototype = {
     delete this._promptActive;
 
     if (this._domWin) {
-      let winUtils = this._domWin.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+      let winUtils = this._domWin.windowUtils;
       winUtils.leaveModalState();
       this.fireDialogEvent(this._domWin, "DOMModalDialogClosed");
     }
@@ -275,8 +275,7 @@ FilePicker.prototype = {
         return;
       let event = aDomWin.document.createEvent("Events");
       event.initEvent(aEventName, true, true);
-      let winUtils = aDomWin.QueryInterface(Ci.nsIInterfaceRequestor)
-                           .getInterface(Ci.nsIDOMWindowUtils);
+      let winUtils = aDomWin.windowUtils;
       winUtils.dispatchEventToChromeOnly(aDomWin, event);
     } catch (ex) {
     }
diff --git a/mobile/android/components/PromptService.js b/mobile/android/components/PromptService.js
index a10554289909..bdaf3a9734dc 100644
--- a/mobile/android/components/PromptService.js
+++ b/mobile/android/components/PromptService.js
@@ -145,7 +145,7 @@ InternalPrompt.prototype = {
   showPrompt: function showPrompt(aPrompt) {
     if (this._domWin) {
       PromptUtils.fireDialogEvent(this._domWin, "DOMWillOpenModalDialog");
-      let winUtils = this._domWin.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+      let winUtils = this._domWin.windowUtils;
       winUtils.enterModalState();
     }
 
@@ -158,7 +158,7 @@ InternalPrompt.prototype = {
     Services.tm.spinEventLoopUntil(() => retval != null);
 
     if (this._domWin) {
-      let winUtils = this._domWin.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+      let winUtils = this._domWin.windowUtils;
       winUtils.leaveModalState();
       PromptUtils.fireDialogEvent(this._domWin, "DOMModalDialogClosed");
     }
@@ -793,8 +793,7 @@ var PromptUtils = {
         return;
       let event = aDomWin.document.createEvent("Events");
       event.initEvent(aEventName, true, true);
-      let winUtils = aDomWin.QueryInterface(Ci.nsIInterfaceRequestor)
-                           .getInterface(Ci.nsIDOMWindowUtils);
+      let winUtils = aDomWin.windowUtils;
       winUtils.dispatchEventToChromeOnly(aDomWin, event);
     } catch (ex) {
     }
diff --git a/mobile/android/components/SessionStore.js b/mobile/android/components/SessionStore.js
index 886725b709de..6839e1530222 100644
--- a/mobile/android/components/SessionStore.js
+++ b/mobile/android/components/SessionStore.js
@@ -937,8 +937,7 @@ SessionStore.prototype = {
 
     // Save the current document resolution.
     let zoom = { value: 1 };
-    content.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(
-      Ci.nsIDOMWindowUtils).getResolution(zoom);
+    content.windowUtils.getResolution(zoom);
     scrolldata.zoom = {};
     scrolldata.zoom.resolution = zoom.value;
     log("onTabScroll() zoom level: " + zoom.value);
@@ -958,8 +957,7 @@ SessionStore.prototype = {
   _getContentViewerSize: function ss_getContentViewerSize(aWindow) {
     let displaySize = {};
     let width = {}, height = {};
-    aWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(
-      Ci.nsIDOMWindowUtils).getContentViewerSize(width, height);
+    aWindow.windowUtils.getContentViewerSize(width, height);
 
     displaySize.width = width.value;
     displaySize.height = height.value;
@@ -1401,8 +1399,7 @@ SessionStore.prototype = {
       log("_restoreZoom(), resolution: " + aScrollData.zoom.resolution +
           ", old displayWidth: " + aScrollData.zoom.displaySize.width);
 
-      let utils = aBrowser.contentWindow.QueryInterface(
-        Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+      let utils = aBrowser.contentWindow.windowUtils;
       // Restore zoom level.
       utils.setRestoreResolution(aScrollData.zoom.resolution,
                                  aScrollData.zoom.displaySize.width,
diff --git a/mobile/android/components/extensions/test/mochitest/test_ext_options_ui.html b/mobile/android/components/extensions/test/mochitest/test_ext_options_ui.html
index 1df653bf23c2..7501cd03b352 100644
--- a/mobile/android/components/extensions/test/mochitest/test_ext_options_ui.html
+++ b/mobile/android/components/extensions/test/mochitest/test_ext_options_ui.html
@@ -27,8 +27,7 @@ async function navigateToAddonDetails(addonId) {
   let rect = item.getBoundingClientRect();
   const x = rect.left + rect.width / 2;
   const y = rect.top + rect.height / 2;
-  let domWinUtils = content.window.QueryInterface(Ci.nsIInterfaceRequestor)
-                           .getInterface(Ci.nsIDOMWindowUtils);
+  let domWinUtils = content.window.windowUtils;
 
   domWinUtils.sendMouseEventToWindow("mousedown", x, y, 0, 1, 0);
   domWinUtils.sendMouseEventToWindow("mouseup", x, y, 0, 1, 0);
diff --git a/mobile/android/components/geckoview/GeckoViewPrompt.js b/mobile/android/components/geckoview/GeckoViewPrompt.js
index 84dec4d81891..083024e05455 100644
--- a/mobile/android/components/geckoview/GeckoViewPrompt.js
+++ b/mobile/android/components/geckoview/GeckoViewPrompt.js
@@ -365,8 +365,7 @@ PromptDelegate.prototype = {
     }
     // Accessing the document object can throw if this window no longer exists. See bug 789888.
     try {
-      let winUtils = this._domWin.QueryInterface(Ci.nsIInterfaceRequestor)
-                                 .getInterface(Ci.nsIDOMWindowUtils);
+      let winUtils = this._domWin.windowUtils;
       if (!aEntering) {
         winUtils.leaveModalState();
       }
diff --git a/mobile/android/modules/geckoview/GeckoViewContent.jsm b/mobile/android/modules/geckoview/GeckoViewContent.jsm
index 228793c65201..ac4d35febf3a 100644
--- a/mobile/android/modules/geckoview/GeckoViewContent.jsm
+++ b/mobile/android/modules/geckoview/GeckoViewContent.jsm
@@ -125,13 +125,11 @@ class GeckoViewContent extends GeckoViewModule {
 
     switch (aMsg.name) {
       case "GeckoView:DOMFullscreenExit":
-        this.window.QueryInterface(Ci.nsIInterfaceRequestor)
-                   .getInterface(Ci.nsIDOMWindowUtils)
+        this.window.windowUtils
                    .remoteFrameFullscreenReverted();
         break;
       case "GeckoView:DOMFullscreenRequest":
-        this.window.QueryInterface(Ci.nsIInterfaceRequestor)
-                   .getInterface(Ci.nsIDOMWindowUtils)
+        this.window.windowUtils
                    .remoteFrameFullscreenChanged(aMsg.target);
         break;
       case "GeckoView:SaveStateFinish":
diff --git a/mobile/android/tests/browser/chrome/test_awsy_lite.html b/mobile/android/tests/browser/chrome/test_awsy_lite.html
index 41ebfcd5d8cf..17c691157c80 100644
--- a/mobile/android/tests/browser/chrome/test_awsy_lite.html
+++ b/mobile/android/tests/browser/chrome/test_awsy_lite.html
@@ -59,7 +59,7 @@
   };
 
   function doFullGc(aCallback, aIterations) {
-    var domWindowUtils = gWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+    var domWindowUtils = gWindow.windowUtils;
 
     function runSoon(f) {
         Services.tm.dispatchToMainThread({ run: f });
diff --git a/mobile/android/tests/browser/chrome/test_session_scroll_position.html b/mobile/android/tests/browser/chrome/test_session_scroll_position.html
index 2caa21d9ee01..21b36c2e44d2 100644
--- a/mobile/android/tests/browser/chrome/test_session_scroll_position.html
+++ b/mobile/android/tests/browser/chrome/test_session_scroll_position.html
@@ -60,9 +60,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1265818
   }
 
   function setZoomLevel(browser, zoom) {
-    browser.contentWindow.QueryInterface(
-      Ci.nsIInterfaceRequestor).getInterface(
-        Ci.nsIDOMWindowUtils).setResolutionAndScaleTo(zoom);
+    browser.contentWindow.windowUtils.setResolutionAndScaleTo(zoom);
   }
 
   // Track the tabs where the tests are happening.
@@ -95,8 +93,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1265818
         yield promiseTabEvent(browser, "SSTabScrollCaptured");
 
         // Check that we've actually scrolled.
-        let ifreq = browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor);
-        let utils = ifreq.getInterface(Ci.nsIDOMWindowUtils);
+        let utils = browser.contentWindow.windowUtils;
         let scrollX = {}, scrollY = {};
         utils.getScrollXY(false, scrollX, scrollY);
         is(scrollX.value, 0, "scrollX set correctly");
@@ -119,8 +116,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1265818
     await promiseBrowserEvent(browser, "AboutReaderContentReady");
 
     // Check the scroll position.
-    let ifreq = browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor);
-    let utils = ifreq.getInterface(Ci.nsIDOMWindowUtils);
+    let utils = browser.contentWindow.windowUtils;
     let scrollX = {}, scrollY = {};
     utils.getScrollXY(false, scrollX, scrollY);
     is(scrollX.value, 0, "scrollX restored correctly");
@@ -145,8 +141,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1265818
         yield promiseTabEvent(browser, "SSTabScrollCaptured");
 
         // Check that we've actually scrolled and zoomed.
-        let ifreq = browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor);
-        let utils = ifreq.getInterface(Ci.nsIDOMWindowUtils);
+        let utils = browser.contentWindow.windowUtils;
         let scrollX = {}, scrollY = {}, zoom = {};
         utils.getResolution(zoom);
         utils.getScrollXY(false, scrollX, scrollY);
@@ -189,8 +184,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1265818
     await scroll;
 
     // Check the scroll position and zoom level.
-    let ifreq = browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor);
-    let utils = ifreq.getInterface(Ci.nsIDOMWindowUtils);
+    let utils = browser.contentWindow.windowUtils;
     let scrollX = {}, scrollY = {}, zoom = {};
     utils.getResolution(zoom);
     utils.getScrollXY(false, scrollX, scrollY);
@@ -232,8 +226,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1265818
         yield promiseTabEvent(browser, "SSTabScrollCaptured");
 
         // Check that we've actually scrolled and zoomed.
-        let ifreq = browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor);
-        let utils = ifreq.getInterface(Ci.nsIDOMWindowUtils);
+        let utils = browser.contentWindow.windowUtils;
         let scrollX = {}, scrollY = {}, zoom = {};
         utils.getResolution(zoom);
         utils.getScrollXY(false, scrollX, scrollY);
@@ -265,8 +258,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1265818
     await promiseBrowserEvent(browser, "pageshow");
 
     // Check the scroll position and zoom level.
-    let ifreq = browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor);
-    let utils = ifreq.getInterface(Ci.nsIDOMWindowUtils);
+    let utils = browser.contentWindow.windowUtils;
     let scrollX = {}, scrollY = {}, zoom = {};
     utils.getResolution(zoom);
     utils.getScrollXY(false, scrollX, scrollY);
diff --git a/mobile/android/tests/browser/robocop/testAccessibleCarets.js b/mobile/android/tests/browser/robocop/testAccessibleCarets.js
index 007908a77436..90eeb6fc0c8b 100644
--- a/mobile/android/tests/browser/robocop/testAccessibleCarets.js
+++ b/mobile/android/tests/browser/robocop/testAccessibleCarets.js
@@ -109,8 +109,7 @@ function getCharPressPoint(doc, element, char, expected) {
  * @return Selection state helper-result object.
  */
 function getLongPressResult(browser, midPoint) {
-  let domWinUtils = browser.contentWindow.
-    QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+  let domWinUtils = browser.contentWindow.windowUtils;
 
   // AccessibleCarets expect longtap between touchstart/end.
   domWinUtils.sendTouchEventToWindow("touchstart", [0], [midPoint.x], [midPoint.y],