What's the name of this mozilla addon?

[Green Island]

Solved
(https://addons.mozilla.org/en-US/firefox/addon/4988)

[namd3r]

I can't find the add-on either, but I do know that the betas of Firefox 3.5 have a button beside the tabs to open a new one, like in your picture.

[Xbehave]

I think the removed it though its not in my 3.5 (ctrl+t) ftw