--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -118,16 +118,61 @@ using namespace mozilla;
 using namespace mozilla::dom;
 using namespace mozilla::ipc;
 using namespace mozilla::layers;
 using namespace mozilla::widget;
 using namespace mozilla::gfx;
 
 class gfxContext;
 
+class OldWindowSize : public LinkedListElement<OldWindowSize>
+{
+public:
+  static void Set(nsIWeakReference* aWindowRef, const nsSize& aSize)
+  {
+    OldWindowSize* item = GetItem(aWindowRef);
+    if (item) {
+      item->mSize = aSize;
+    } else {
+      item = new OldWindowSize(aWindowRef, aSize);
+      sList.insertBack(item);
+    }
+  }
+
+  static nsSize GetAndRemove(nsIWeakReference* aWindowRef)
+  {
+    nsSize result;
+    if (OldWindowSize* item = GetItem(aWindowRef)) {
+      result = item->mSize;
+      delete item;
+    }
+    return result;
+  }
+
+private:
+  explicit OldWindowSize(nsIWeakReference* aWindowRef, const nsSize& aSize)
+    : mWindowRef(aWindowRef), mSize(aSize) { }
+  ~OldWindowSize() { };
+
+  static OldWindowSize* GetItem(nsIWeakReference* aWindowRef)
+  {
+    OldWindowSize* item = sList.getFirst();
+    while (item && item->mWindowRef != aWindowRef) {
+      item = item->getNext();
+    }
+    return item;
+  }
+
+  static LinkedList<OldWindowSize> sList;
+  nsWeakPtr mWindowRef;
+  nsSize mSize;
+};
+
+LinkedList<OldWindowSize> OldWindowSize::sList;
+
 NS_INTERFACE_MAP_BEGIN(nsDOMWindowUtils)
   NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIDOMWindowUtils)
   NS_INTERFACE_MAP_ENTRY(nsIDOMWindowUtils)
   NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
 NS_INTERFACE_MAP_END
 
 NS_IMPL_ADDREF(nsDOMWindowUtils)
 NS_IMPL_RELEASE(nsDOMWindowUtils)
@@ -136,16 +181,17 @@ nsDOMWindowUtils::nsDOMWindowUtils(nsGlo
 {
   nsCOMPtr<nsISupports> supports = do_QueryObject(aWindow);
   mWindow = do_GetWeakReference(supports);
   NS_ASSERTION(aWindow->IsOuterWindow(), "How did that happen?");
 }
 
 nsDOMWindowUtils::~nsDOMWindowUtils()
 {
+  OldWindowSize::GetAndRemove(mWindow);
 }
 
 nsIPresShell*
 nsDOMWindowUtils::GetPresShell()
 {
   nsCOMPtr<nsPIDOMWindowOuter> window = do_QueryReferent(mWindow);
   if (!window)
     return nullptr;
@@ -3099,61 +3145,16 @@ PrepareForFullscreenChange(nsIPresShell*
       if (aOldSize) {
         viewManager->GetWindowDimensions(&aOldSize->width, &aOldSize->height);
       }
       viewManager->SetWindowDimensions(aSize.width, aSize.height);
     }
   }
 }
 
-class OldWindowSize : public LinkedListElement<OldWindowSize>
-{
-public:
-  static void Set(nsIWeakReference* aWindowRef, const nsSize& aSize)
-  {
-    OldWindowSize* item = GetItem(aWindowRef);
-    if (item) {
-      item->mSize = aSize;
-    } else {
-      item = new OldWindowSize(aWindowRef, aSize);
-      sList.insertBack(item);
-    }
-  }
-
-  static nsSize GetAndRemove(nsIWeakReference* aWindowRef)
-  {
-    nsSize result;
-    if (OldWindowSize* item = GetItem(aWindowRef)) {
-      result = item->mSize;
-      delete item;
-    }
-    return result;
-  }
-
-private:
-  explicit OldWindowSize(nsIWeakReference* aWindowRef, const nsSize& aSize)
-    : mWindowRef(aWindowRef), mSize(aSize) { }
-  ~OldWindowSize() { };
-
-  static OldWindowSize* GetItem(nsIWeakReference* aWindowRef)
-  {
-    OldWindowSize* item = sList.getFirst();
-    while (item && item->mWindowRef != aWindowRef) {
-      item = item->getNext();
-    }
-    return item;
-  }
-
-  static LinkedList<OldWindowSize> sList;
-  nsWeakPtr mWindowRef;
-  nsSize mSize;
-};
-
-LinkedList<OldWindowSize> OldWindowSize::sList;
-
 NS_IMETHODIMP
 nsDOMWindowUtils::HandleFullscreenRequests(bool* aRetVal)
 {
   PROFILER_MARKER("Enter fullscreen");
   nsCOMPtr<nsIDocument> doc = GetDocument();
   NS_ENSURE_STATE(doc);
 
   // Notify the pres shell that we are starting fullscreen change, and