--- a/dom/canvas/WebGLTimerQuery.cpp
+++ b/dom/canvas/WebGLTimerQuery.cpp
@@ -58,18 +58,25 @@ WebGLContext*
 WebGLTimerQuery::GetParentObject() const
 {
   return mContext;
 }
 
 void
 WebGLTimerQuery::QueueAvailablity()
 {
-  RefPtr<WebGLTimerQuery> self = this;
-  NS_DispatchToCurrentThread(NS_NewRunnableFunction([self] { self->mCanBeAvailable = true; }));
+  WeakPtr<WebGLTimerQuery> weakPtr = this;
+
+  const auto fnMakeAvailable = [weakPtr]() { // Copy the WeakPtr.
+    if (weakPtr) {
+      weakPtr->mCanBeAvailable = true;
+    }
+  };
+
+  NS_DispatchToCurrentThread(NS_NewRunnableFunction(fnMakeAvailable));
 }
 
 NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(WebGLTimerQuery)
 
 NS_IMPL_CYCLE_COLLECTION_ROOT_NATIVE(WebGLTimerQuery, AddRef)
 NS_IMPL_CYCLE_COLLECTION_UNROOT_NATIVE(WebGLTimerQuery, Release)
 
 } // namespace mozilla

--- a/dom/canvas/WebGLTimerQuery.h
+++ b/dom/canvas/WebGLTimerQuery.h
@@ -13,28 +13,30 @@
 
 namespace mozilla {
 
 class WebGLTimerQuery final
   : public nsWrapperCache
   , public WebGLRefCountedObject<WebGLTimerQuery>
   , public LinkedListElement<WebGLTimerQuery>
   , public WebGLContextBoundObject
+  , public SupportsWeakPtr<WebGLTimerQuery>
 {
   friend class WebGLExtensionDisjointTimerQuery;
 
 public:
   const GLenum mGLName;
 protected:
   GLenum mTarget;
   bool mCanBeAvailable;
 
 public:
   NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(WebGLTimerQuery)
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(WebGLTimerQuery)
+  MOZ_DECLARE_WEAKREFERENCE_TYPENAME(WebGLTimerQuery)
 
   static WebGLTimerQuery* Create(WebGLContext* webgl);
 
 private:
   explicit WebGLTimerQuery(WebGLContext* webgl, GLuint name);
   ~WebGLTimerQuery();
 
   void Delete();