Bug 774201 - Avoid pointer to integer cast losing precision on win64 r=billm

dom/base/nsJSEnvironment.cpp

@@ -3747,7 +3747,7 @@ SetMemoryGCPrefChangedCallback(const char* aPrefName, void* aClosure)
   PRInt32 pref = Preferences::GetInt(aPrefName, -1);
   // handle overflow and negative pref values
   if (pref > 0 && pref < 10000)
-    JS_SetGCParameter(nsJSRuntime::sRuntime, (JSGCParamKey)(long)aClosure, pref);
+    JS_SetGCParameter(nsJSRuntime::sRuntime, (JSGCParamKey)(intptr_t)aClosure, pref);
   return 0;
 }