diff -r 000000000000 -r 6474c204b198 toolkit/components/places/nsMaybeWeakPtr.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/places/nsMaybeWeakPtr.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,80 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsMaybeWeakPtr.h"
+
+void*
+nsMaybeWeakPtr_base::GetValueAs(const nsIID &iid) const
+{
+  nsresult rv;
+  void *ref;
+  if (mPtr) {
+    rv = mPtr->QueryInterface(iid, &ref);
+    if (NS_SUCCEEDED(rv)) {
+      return ref;
+    }
+  }
+
+  nsCOMPtr<nsIWeakReference> weakRef = do_QueryInterface(mPtr);
+  if (weakRef) {
+    rv = weakRef->QueryReferent(iid, &ref);
+    if (NS_SUCCEEDED(rv)) {
+      return ref;
+    }
+  }
+
+  return nullptr;
+}
+
+nsresult
+NS_AppendWeakElementBase(isupports_array_type *aArray,
+                         nsISupports *aElement,
+                         bool aOwnsWeak)
+{
+  nsCOMPtr<nsISupports> ref;
+  if (aOwnsWeak) {
+    nsCOMPtr<nsIWeakReference> weakRef;
+    weakRef = do_GetWeakReference(aElement);
+    reinterpret_cast<nsCOMPtr<nsISupports>*>(&weakRef)->swap(ref);
+  } else {
+    ref = aElement;
+  }
+
+  if (aArray->IndexOf(ref) != aArray->NoIndex) {
+    return NS_ERROR_INVALID_ARG; // already present
+  }
+  if (!aArray->AppendElement(ref)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  return NS_OK;
+}
+
+nsresult
+NS_RemoveWeakElementBase(isupports_array_type *aArray,
+                         nsISupports *aElement)
+{
+  uint32_t index = aArray->IndexOf(aElement);
+  if (index != aArray->NoIndex) {
+    aArray->RemoveElementAt(index);
+    return NS_OK;
+  }
+
+  // Don't use do_GetWeakReference; it should only be called if we know
+  // the object supports weak references.
+  nsCOMPtr<nsISupportsWeakReference> supWeakRef = do_QueryInterface(aElement);
+  NS_ENSURE_TRUE(supWeakRef, NS_ERROR_INVALID_ARG);
+
+  nsCOMPtr<nsIWeakReference> weakRef;
+  nsresult rv = supWeakRef->GetWeakReference(getter_AddRefs(weakRef));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  index = aArray->IndexOf(weakRef);
+  if (index == aArray->NoIndex) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  aArray->RemoveElementAt(index);
+  return NS_OK;
+}