Looks interesting, I've got a couple of user scripts I was considering turning into an extension, this looks like it'll make that simpler to start working on. Thanks :)
Sightly OT: The main thing keeping me from switching away from Firefox is the lack of an extension-usable sidebar in Chromium, preventing a <i>usable</i> tree style tab implementation.<p>Chromium does have a sidebar displaying web content now (reading list/new side search feature), but they just won't let extensions use it.