Per spec, these should be just vanilla objects, whose proto is Object.prototype. Right now we create a callable object whose proto is Function.prototype.

Comment on attachment 686389 [details] [diff] [review] Create vanilla objects for the interface object of callback interfaces. Review of attachment 686389 [details] [diff] [review]: ----------------------------------------------------------------- ::: dom/bindings/Codegen.py @@ +1465,1 @@ > constructHook = "&" + CONSTRUCT_HOOK_NAME + "_holder" I know you're just changing existing code, but needConstructor seems badly named here :-/. I think it would make more sense to rename needsConstructorFunction to needsConstructHookHolder or something and do: if (needInterfaceObject and self.descriptor.needsConstructHookHolder(): constructHookHolder = "&" + CONSTRUCT_HOOK_NAME + "_holder" else: constructHookHolder = "nullptr" and pass that in to the call to CreateInterfaceObjects.

https://hg.mozilla.org/integration/mozilla-inbound/rev/d531b6a61a6e with that change. Once we turn on WebIDL bindings for NodeFilter this will be tested too (that's how I found it).