Great start! Rated 5 out of 5 stars
This looks like a very useful tool. I've played with it a little for Firefox add-on development. Its :chrome mode gives me an easy way to see or modify my add-on's data. I can also learn about what data Firefox stores under the 'window' and 'gBrowser' objects.
It could still use some more features (and I filed a couple SUGs on his bug tracker), but it's already a great start.
(Tested in Firefox nightly 17.0a1.)