diff --git a/toolkit/devtools/LayoutHelpers.jsm b/toolkit/devtools/LayoutHelpers.jsm
index 970dfd1c38f..38092142c50 100644
--- a/toolkit/devtools/LayoutHelpers.jsm
+++ b/toolkit/devtools/LayoutHelpers.jsm
@@ -13,14 +13,15 @@ Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Services",
   "resource://gre/modules/Services.jsm");
 
-XPCOMUtils.defineLazyGetter(this, "PlatformKeys", function() {
-  return Services.strings.createBundle(
-    "chrome://global-platform/locale/platformKeys.properties");
-});
-
 this.EXPORTED_SYMBOLS = ["LayoutHelpers"];
 
-this.LayoutHelpers = LayoutHelpers = {
+this.LayoutHelpers = LayoutHelpers = function(aTopLevelWindow) {
+  this._topDocShell = aTopLevelWindow.QueryInterface(Ci.nsIInterfaceRequestor)
+                                     .getInterface(Ci.nsIWebNavigation)
+                                     .QueryInterface(Ci.nsIDocShell);
+}
+
+LayoutHelpers.prototype = {
 
   /**
    * Compute the position and the dimensions for the visible portion
@@ -70,22 +71,27 @@ this.LayoutHelpers = LayoutHelpers = {
       // Selection has been clipped to fit in its own window.
 
       // Are we in the top-level window?
-      if (frameWin.parent === frameWin || !frameWin.frameElement) {
+      if (this.isTopLevelWindow(frameWin)) {
+        break;
+      }
+
+      let frameElement = this.getFrameElement(frameWin);
+      if (!frameElement) {
         break;
       }
 
       // We are in an iframe.
       // We take into account the parent iframe position and its
       // offset (borders and padding).
-      let frameRect = frameWin.frameElement.getBoundingClientRect();
+      let frameRect = frameElement.getBoundingClientRect();
 
       let [offsetTop, offsetLeft] =
-        this.getIframeContentOffset(frameWin.frameElement);
+        this.getIframeContentOffset(frameElement);
 
       rect.top += frameRect.top + offsetTop;
       rect.left += frameRect.left + offsetLeft;
 
-      frameWin = frameWin.parent;
+      frameWin = this.getParentWindow(frameWin);
     }
 
     return rect;
@@ -115,22 +121,27 @@ this.LayoutHelpers = LayoutHelpers = {
     while (true) {
 
       // Are we in the top-level window?
-      if (frameWin.parent === frameWin || !frameWin.frameElement) {
+      if (this.isTopLevelWindow(frameWin)) {
+        break;
+      }
+
+      let frameElement = this.getFrameElement(frameWin);
+      if (!frameElement) {
         break;
       }
 
       // We are in an iframe.
       // We take into account the parent iframe position and its
       // offset (borders and padding).
-      let frameRect = frameWin.frameElement.getBoundingClientRect();
+      let frameRect = frameElement.getBoundingClientRect();
 
       let [offsetTop, offsetLeft] =
-        this.getIframeContentOffset(frameWin.frameElement);
+        this.getIframeContentOffset(frameElement);
 
       rect.top += frameRect.top + offsetTop;
       rect.left += frameRect.left + offsetLeft;
 
-      frameWin = frameWin.parent;
+      frameWin = this.getParentWindow(frameWin);
     }
 
     return rect;
@@ -203,7 +214,7 @@ this.LayoutHelpers = LayoutHelpers = {
         let rect = node.getBoundingClientRect();
 
         // Gap between the iframe and its content window.
-        let [offsetTop, offsetLeft] = LayoutHelpers.getIframeContentOffset(node);
+        let [offsetTop, offsetLeft] = this.getIframeContentOffset(node);
 
         aX -= rect.left + offsetLeft;
         aY -= rect.top + offsetTop;
@@ -296,9 +307,10 @@ this.LayoutHelpers = LayoutHelpers = {
       }
     }
 
-    if (win.parent !== win) {
+    if (!this.isTopLevelWindow(win)) {
       // We are inside an iframe.
-      LH_scrollIntoViewIfNeeded(win.frameElement, centered);
+      let frameElement = this.getFrameElement(win);
+      this.scrollIntoViewIfNeeded(frameElement, centered);
     }
   },
 
@@ -322,63 +334,60 @@ this.LayoutHelpers = LayoutHelpers = {
   },
 
   /**
-   * Prettifies the modifier keys for an element.
-   *
-   * @param Node aElemKey
-   *        The key element to get the modifiers from.
-   * @param boolean aAllowCloverleaf
-   *        Pass true to use the cloverleaf symbol instead of a descriptive string.
-   * @return string
-   *         A prettified and properly separated modifier keys string.
+   * like win.parent === win, but goes through mozbrowsers and mozapps iframes.
    */
-  prettyKey: function LH_prettyKey(aElemKey, aAllowCloverleaf)
-  {
-    let elemString = "";
-    let elemMod = aElemKey.getAttribute("modifiers");
+  isTopLevelWindow: function LH_isTopLevelWindow(win) {
+    let docShell = win.QueryInterface(Ci.nsIInterfaceRequestor)
+                   .getInterface(Ci.nsIWebNavigation)
+                   .QueryInterface(Ci.nsIDocShell);
 
-    if (elemMod.match("accel")) {
-      if (Services.appinfo.OS == "Darwin") {
-        // XXX bug 779642 Use "Cmd-" literal vs. cloverleaf meta-key until
-        // Orion adds variable height lines.
-        if (!aAllowCloverleaf) {
-          elemString += "Cmd-";
-        } else {
-          elemString += PlatformKeys.GetStringFromName("VK_META") +
-                        PlatformKeys.GetStringFromName("MODIFIER_SEPARATOR");
+    return docShell === this._topDocShell;
+  },
+
+  /**
+   * like win.parent, but goes through mozbrowsers and mozapps iframes.
+   */
+  getParentWindow: function LH_getParentWindow(win) {
+    if (this.isTopLevelWindow(win)) {
+      return null;
+    }
+
+    let docShell = win.QueryInterface(Ci.nsIInterfaceRequestor)
+                   .getInterface(Ci.nsIWebNavigation)
+                   .QueryInterface(Ci.nsIDocShell);
+
+    if (docShell.isBrowserOrApp) {
+      let parentDocShell = docShell.getSameTypeParentIgnoreBrowserAndAppBoundaries();
+      return parentDocShell.contentViewer.DOMDocument.defaultView;
+    } else {
+      return win.parent;
+    }
+  },
+
+  /**
+   * like win.frameElement, but goes through mozbrowsers and mozapps iframes.
+   */
+  getFrameElement: function LH_getFrameElement(win) {
+    if (this.isTopLevelWindow(win)) {
+      return null;
+    }
+
+    let docShell = win.QueryInterface(Ci.nsIInterfaceRequestor)
+                   .getInterface(Ci.nsIWebNavigation)
+                   .QueryInterface(Ci.nsIDocShell);
+
+    if (docShell.isBrowserOrApp) {
+      let parentDocShell = docShell.getSameTypeParentIgnoreBrowserAndAppBoundaries();
+      let parentDoc = parentDocShell.contentViewer.DOMDocument;
+      let allIframes = parentDoc.querySelectorAll("iframe");
+      for (let f of allIframes) {
+        if (f.contentWindow === win) {
+          return f;
         }
-      } else {
-        elemString += PlatformKeys.GetStringFromName("VK_CONTROL") +
-                      PlatformKeys.GetStringFromName("MODIFIER_SEPARATOR");
       }
+      return null;
+    } else {
+      return win.frameElement;
     }
-    if (elemMod.match("access")) {
-      if (Services.appinfo.OS == "Darwin") {
-        elemString += PlatformKeys.GetStringFromName("VK_CONTROL") +
-                      PlatformKeys.GetStringFromName("MODIFIER_SEPARATOR");
-      } else {
-        elemString += PlatformKeys.GetStringFromName("VK_ALT") +
-                      PlatformKeys.GetStringFromName("MODIFIER_SEPARATOR");
-      }
-    }
-    if (elemMod.match("shift")) {
-      elemString += PlatformKeys.GetStringFromName("VK_SHIFT") +
-                    PlatformKeys.GetStringFromName("MODIFIER_SEPARATOR");
-    }
-    if (elemMod.match("alt")) {
-      elemString += PlatformKeys.GetStringFromName("VK_ALT") +
-                    PlatformKeys.GetStringFromName("MODIFIER_SEPARATOR");
-    }
-    if (elemMod.match("ctrl") || elemMod.match("control")) {
-      elemString += PlatformKeys.GetStringFromName("VK_CONTROL") +
-                    PlatformKeys.GetStringFromName("MODIFIER_SEPARATOR");
-    }
-    if (elemMod.match("meta")) {
-      elemString += PlatformKeys.GetStringFromName("VK_META") +
-                    PlatformKeys.GetStringFromName("MODIFIER_SEPARATOR");
-    }
-
-    return elemString +
-      (aElemKey.getAttribute("keycode").replace(/^.*VK_/, "") ||
-       aElemKey.getAttribute("key")).toUpperCase();
-  }
+  },
 };