--- a/xpcom/glue/nsProxyRelease.h
+++ b/xpcom/glue/nsProxyRelease.h
@@ -267,14 +267,18 @@ public:
   // These are safe to call on other threads with appropriate external locking.
   bool operator==(const nsMainThreadPtrHandle<T>& aOther) const
   {
     if (!mPtr || !aOther.mPtr) {
       return mPtr == aOther.mPtr;
     }
     return *mPtr == *aOther.mPtr;
   }
+  bool operator!=(const nsMainThreadPtrHandle<T>& aOther) const
+  {
+    return !operator==(aOther);
+  }
   bool operator!() const {
     return !mPtr || !*mPtr;
   }
 };
 
 #endif