diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index 96780f90bc8..29d35dcbc50 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -1550,3 +1550,12 @@ nsDOMWindowUtils::GetCursorType(PRInt16 *aCursor)
 
   return NS_OK;
 }
+
+NS_IMETHODIMP
+nsDOMWindowUtils::GetOuterWindowWithId(PRUint64 aWindowID,
+                                       nsIDOMWindow** aWindow)
+{
+  *aWindow = nsGlobalWindow::GetOuterWindowWithId(aWindowID);
+  NS_IF_ADDREF(*aWindow);
+  return NS_OK;
+}
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 53935410895..a446862b70e 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -242,6 +242,7 @@ using mozilla::TimeStamp;
 using mozilla::TimeDuration;
 
 nsIDOMStorageList *nsGlobalWindow::sGlobalStorageList  = nsnull;
+nsGlobalWindow::WindowByIdTable *nsGlobalWindow::sOuterWindowsById = nsnull;
 
 static nsIEntropyCollector *gEntropyCollector          = nsnull;
 static PRInt32              gRefCnt                    = 0;
@@ -773,6 +774,18 @@ nsGlobalWindow::nsGlobalWindow(nsGlobalWindow *aOuterWindow)
 
     mObserver = nsnull;
     SetIsProxy();
+
+    if (!sOuterWindowsById) {
+      sOuterWindowsById = new WindowByIdTable();
+      if (!sOuterWindowsById->Init()) {
+        delete sOuterWindowsById;
+        sOuterWindowsById = nsnull;
+      }
+    }
+
+    if (sOuterWindowsById) {
+      sOuterWindowsById->Put(mWindowID, this);
+    }
   }
 
   // We could have failed the first time through trying
@@ -825,8 +838,13 @@ nsGlobalWindow::nsGlobalWindow(nsGlobalWindow *aOuterWindow)
 
 nsGlobalWindow::~nsGlobalWindow()
 {
+  if (sOuterWindowsById) {
+    sOuterWindowsById->Remove(mWindowID);
+  }
   if (!--gRefCnt) {
     NS_IF_RELEASE(gEntropyCollector);
+    delete sOuterWindowsById;
+    sOuterWindowsById = nsnull;
   }
 #ifdef DEBUG
   nsCAutoString url;
diff --git a/dom/base/nsGlobalWindow.h b/dom/base/nsGlobalWindow.h
index 6ff563f9701..7e818d0adb4 100644
--- a/dom/base/nsGlobalWindow.h
+++ b/dom/base/nsGlobalWindow.h
@@ -562,6 +562,10 @@ public:
     return mSerial;
   }
 
+  static nsGlobalWindow* GetOuterWindowWithId(PRUint64 aWindowID) {
+    return sOuterWindowsById ? sOuterWindowsById->Get(aWindowID) : nsnull;
+  }
+
 protected:
   // Object Management
   virtual ~nsGlobalWindow();
@@ -946,6 +950,9 @@ protected:
   friend class nsDOMWindowUtils;
   friend class PostMessageEvent;
   static nsIDOMStorageList* sGlobalStorageList;
+
+  typedef nsDataHashtable<nsUint64HashKey, nsGlobalWindow*> WindowByIdTable;
+  static WindowByIdTable* sOuterWindowsById;
 };
 
 /*
diff --git a/dom/interfaces/base/nsIDOMWindowUtils.idl b/dom/interfaces/base/nsIDOMWindowUtils.idl
index 3663922fda1..be32608809c 100644
--- a/dom/interfaces/base/nsIDOMWindowUtils.idl
+++ b/dom/interfaces/base/nsIDOMWindowUtils.idl
@@ -59,8 +59,9 @@ interface nsIDOMHTMLCanvasElement;
 interface nsIDOMEvent;
 interface nsITransferable;
 interface nsIQueryContentEventResult;
+interface nsIDOMWindow;
 
-[scriptable, uuid(43fd9eb5-9e08-4d60-a305-3f87b1d5c398)]
+[scriptable, uuid(33cbae2d-2361-4f3d-b589-cc55af07a434)]
 interface nsIDOMWindowUtils : nsISupports {
 
   /**
@@ -789,6 +790,11 @@ interface nsIDOMWindowUtils : nsISupports {
    */
   readonly attribute AString layerManagerType;
 
+  /**
+   * Return the outer window with the given ID, if any.  Can return null.
+   */
+  nsIDOMWindow getOuterWindowWithId(in unsigned long long aOuterWindowID);
+
 %{C++
   virtual nsresult RenderDocument(const nsRect& aRect,
                                   PRUint32 aFlags,
diff --git a/xpcom/glue/nsHashKeys.h b/xpcom/glue/nsHashKeys.h
index 4c199b54b8d..09a955576bf 100644
--- a/xpcom/glue/nsHashKeys.h
+++ b/xpcom/glue/nsHashKeys.h
@@ -59,6 +59,7 @@
  * nsStringHashKey
  * nsCStringHashKey
  * nsUint32HashKey
+ * nsUint64HashKey
  * nsPtrHashkey
  * nsClearingPtrHashKey
  * nsVoidPtrHashKey
@@ -164,6 +165,32 @@ private:
   const PRUint32 mValue;
 };
 
+/**
+ * hashkey wrapper using PRUint64 KeyType
+ *
+ * @see nsTHashtable::EntryType for specification
+ */
+class nsUint64HashKey : public PLDHashEntryHdr
+{
+public:
+  typedef const PRUint64& KeyType;
+  typedef const PRUint64* KeyTypePointer;
+  
+  nsUint64HashKey(KeyTypePointer aKey) : mValue(*aKey) { }
+  nsUint64HashKey(const nsUint64HashKey& toCopy) : mValue(toCopy.mValue) { }
+  ~nsUint64HashKey() { }
+
+  KeyType GetKey() const { return mValue; }
+  PRBool KeyEquals(KeyTypePointer aKey) const { return *aKey == mValue; }
+
+  static KeyTypePointer KeyToPointer(KeyType aKey) { return &aKey; }
+  static PLDHashNumber HashKey(KeyTypePointer aKey) { return *aKey; }
+  enum { ALLOW_MEMMOVE = PR_TRUE };
+
+private:
+  const PRUint64 mValue;
+};
+
 /**
  * hashkey wrapper using nsISupports* KeyType
  *