--- a/xpcom/glue/nsProxyRelease.h
+++ b/xpcom/glue/nsProxyRelease.h
@@ -131,16 +131,18 @@ public:
     // Nobody should be touching the raw pointer off-main-thread.
     if (MOZ_UNLIKELY(!NS_IsMainThread())) {
       NS_ERROR("Can't dereference nsMainThreadPtrHolder off main thread");
       MOZ_CRASH();
     }
     return mRawPtr;
   }
 
+  bool operator==(const nsMainThreadPtrHolder<T>& aOther) const { return mRawPtr == aOther.mRawPtr; }
+
   NS_IMETHOD_(nsrefcnt) Release();
   NS_IMETHOD_(nsrefcnt) AddRef();
 
 private:
   // This class is threadsafe and reference-counted.
   nsAutoRefCnt mRefCnt;
 
   // Our wrapped pointer.
@@ -158,16 +160,17 @@ template<class T>
 NS_IMPL_THREADSAFE_RELEASE(nsMainThreadPtrHolder<T>)
 
 template<class T>
 class nsMainThreadPtrHandle
 {
   nsRefPtr<nsMainThreadPtrHolder<T> > mPtr;
 
   public:
+  nsMainThreadPtrHandle() : mPtr(NULL) {}
   nsMainThreadPtrHandle(nsMainThreadPtrHolder<T> *aHolder) : mPtr(aHolder) {}
   nsMainThreadPtrHandle(const nsMainThreadPtrHandle& aOther) : mPtr(aOther.mPtr) {}
   nsMainThreadPtrHandle& operator=(const nsMainThreadPtrHandle& aOther) {
     mPtr = aOther.mPtr;
     return *this;
   }
 
   operator nsMainThreadPtrHolder<T>*() { return mPtr.get(); }
@@ -178,13 +181,30 @@ class nsMainThreadPtrHandle
   T* get()
   {
     MOZ_ASSERT(NS_IsMainThread());
     if (mPtr) {
       return mPtr.get()->get();
     }
     return nullptr;
   }
+  const T* get() const
+  {
+    MOZ_ASSERT(NS_IsMainThread());
+    if (mPtr) {
+      return mPtr.get()->get();
+    }
+    return nullptr;
+  }
+
   operator T*() { return get(); }
   T* operator->() { return get(); }
+
+  // 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!() { return !mPtr; }
 };
 
 #endif