The extension API for Firefox was simply the entire internal api of the browser. Making it work cross process (everything was single process) was a huge pain an

The extension API for Firefox was simply the entire internal api of the browser. Making it work cross process (everything was single process) was a huge pain and things were going to break depending on how you used the APIs. And the security considerations of accessing every api was a big issue. On the other hand, Firebug could not have been created without it…