--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -1846,16 +1846,17 @@ jsid nsDOMClassInfo::sName_id           
 jsid nsDOMClassInfo::sScrollX_id         = JSID_VOID;
 jsid nsDOMClassInfo::sScrollY_id         = JSID_VOID;
 jsid nsDOMClassInfo::sScrollMaxX_id      = JSID_VOID;
 jsid nsDOMClassInfo::sScrollMaxY_id      = JSID_VOID;
 jsid nsDOMClassInfo::sItem_id            = JSID_VOID;
 jsid nsDOMClassInfo::sNamedItem_id       = JSID_VOID;
 jsid nsDOMClassInfo::sEnumerate_id       = JSID_VOID;
 jsid nsDOMClassInfo::sNavigator_id       = JSID_VOID;
+jsid nsDOMClassInfo::sTop_id             = JSID_VOID;
 jsid nsDOMClassInfo::sDocument_id        = JSID_VOID;
 jsid nsDOMClassInfo::sFrames_id          = JSID_VOID;
 jsid nsDOMClassInfo::sSelf_id            = JSID_VOID;
 jsid nsDOMClassInfo::sOpener_id          = JSID_VOID;
 jsid nsDOMClassInfo::sAll_id             = JSID_VOID;
 jsid nsDOMClassInfo::sTags_id            = JSID_VOID;
 jsid nsDOMClassInfo::sAddEventListener_id= JSID_VOID;
 jsid nsDOMClassInfo::sBaseURIObject_id   = JSID_VOID;
@@ -2125,16 +2126,17 @@ nsDOMClassInfo::DefineStaticJSVals(JSCon
   SET_JSID_TO_STRING(sScrollX_id,         cx, "scrollX");
   SET_JSID_TO_STRING(sScrollY_id,         cx, "scrollY");
   SET_JSID_TO_STRING(sScrollMaxX_id,      cx, "scrollMaxX");
   SET_JSID_TO_STRING(sScrollMaxY_id,      cx, "scrollMaxY");
   SET_JSID_TO_STRING(sItem_id,            cx, "item");
   SET_JSID_TO_STRING(sNamedItem_id,       cx, "namedItem");
   SET_JSID_TO_STRING(sEnumerate_id,       cx, "enumerateProperties");
   SET_JSID_TO_STRING(sNavigator_id,       cx, "navigator");
+  SET_JSID_TO_STRING(sTop_id,             cx, "top");
   SET_JSID_TO_STRING(sDocument_id,        cx, "document");
   SET_JSID_TO_STRING(sFrames_id,          cx, "frames");
   SET_JSID_TO_STRING(sSelf_id,            cx, "self");
   SET_JSID_TO_STRING(sOpener_id,          cx, "opener");
   SET_JSID_TO_STRING(sAll_id,             cx, "all");
   SET_JSID_TO_STRING(sTags_id,            cx, "tags");
   SET_JSID_TO_STRING(sAddEventListener_id,cx, "addEventListener");
   SET_JSID_TO_STRING(sBaseURIObject_id,   cx, "baseURIObject");
@@ -5241,16 +5243,17 @@ nsDOMClassInfo::ShutDown()
   sName_id            = JSID_VOID;
   sScrollX_id         = JSID_VOID;
   sScrollY_id         = JSID_VOID;
   sScrollMaxX_id      = JSID_VOID;
   sScrollMaxY_id      = JSID_VOID;
   sItem_id            = JSID_VOID;
   sEnumerate_id       = JSID_VOID;
   sNavigator_id       = JSID_VOID;
+  sTop_id             = JSID_VOID;
   sDocument_id        = JSID_VOID;
   sFrames_id          = JSID_VOID;
   sSelf_id            = JSID_VOID;
   sOpener_id          = JSID_VOID;
   sAll_id             = JSID_VOID;
   sTags_id            = JSID_VOID;
   sAddEventListener_id= JSID_VOID;
   sBaseURIObject_id   = JSID_VOID;
@@ -7345,16 +7348,39 @@ nsWindowSH::NewResolve(nsIXPConnectWrapp
                                    JSPROP_ENUMERATE)) {
         return NS_ERROR_FAILURE;
       }
       *objp = obj;
 
       return NS_OK;
     }
 
+    if (sTop_id == id) {
+      nsCOMPtr<nsIDOMWindow> top;
+      rv = win->GetScriptableTop(getter_AddRefs(top));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      jsval v;
+      nsCOMPtr<nsIXPConnectJSObjectHolder> holder;
+      rv = WrapNative(cx, obj, top, &NS_GET_IID(nsIDOMWindow), true,
+                      &v, getter_AddRefs(holder));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // Hold on to the top window object as a global property so we
+      // don't need to worry about losing expando properties etc.
+      if (!::JS_DefinePropertyById(cx, obj, id, v, nullptr, nullptr,
+                                   JSPROP_READONLY | JSPROP_PERMANENT |
+                                   JSPROP_ENUMERATE)) {
+        return NS_ERROR_FAILURE;
+      }
+      *objp = obj;
+
+      return NS_OK;
+    }
+
     if (sDocument_id == id) {
       nsCOMPtr<nsIDocument> document = win->GetDoc();
       JS::Value v;
       nsCOMPtr<nsIXPConnectJSObjectHolder> holder;
       rv = WrapNative(cx, JS_GetGlobalForScopeChain(cx), document, document,
                       &NS_GET_IID(nsIDOMDocument), &v, getter_AddRefs(holder),
                       false);
       NS_ENSURE_SUCCESS(rv, rv);

--- a/dom/base/nsDOMClassInfo.h
+++ b/dom/base/nsDOMClassInfo.h
@@ -238,16 +238,17 @@ public:
   static jsid sScrollX_id;
   static jsid sScrollY_id;
   static jsid sScrollMaxX_id;
   static jsid sScrollMaxY_id;
   static jsid sItem_id;
   static jsid sNamedItem_id;
   static jsid sEnumerate_id;
   static jsid sNavigator_id;
+  static jsid sTop_id;
   static jsid sDocument_id;
   static jsid sFrames_id;
   static jsid sSelf_id;
   static jsid sOpener_id;
   static jsid sAll_id;
   static jsid sTags_id;
   static jsid sAddEventListener_id;
   static jsid sBaseURIObject_id;