Firefox Addon SDK onMouseover Event for a Button

Question

With the coming of multi-process Firefox, I have decided to revamp my addon. It is a toolbar addon that was built on XUL. Now I want to build it using the Addon SDK.

Answer 1

First of all, error message you're getting already tells you how to make it work.

But it's not necessarily what you need anyway, usually sdk/view/core provides access to the underlying XUL elements through one of its 3 methods.