Bug 965921 - Handle addons that expose JS-implemented XPCOM components to content. r=mrbkap

js/xpconnect/src/XPCWrappedNativeJSOps.cpp

@@ -155,9 +155,12 @@ XPC_WN_DoubleWrappedGetter(JSContext *cx, unsigned argc, jsval *vp)
         return true;
     }
 
-    // It is a double wrapped object. This should never appear in content these
-    // days, but let's be safe here.
-    MOZ_RELEASE_ASSERT(nsContentUtils::IsCallerChrome());
+    // It is a double wrapped object. This should really never appear in
+    // content these days, but addons still do it - see bug 965921.
+    if (MOZ_UNLIKELY(!nsContentUtils::IsCallerChrome())) {
+        JS_ReportError(cx, "Attempt to use .wrappedJSObject in untrusted code");
+        return false;
+    }
     args.rval().setObject(*realObject);
     return JS_WrapValue(cx, args.rval());
 }