been playing around and tweaking stuff in firefox this past week and also played with tha add-on you linked to for the tree tabs. thought it was pretty cool but didnt play too nice with my theme and the auto bookmarks hider. when i hovered / activated the tree tabs, my bookmarks toolbar would drop down! LOLOL!!!
(inspired by a screenshot that Scott sent me the other day while we worked on something else)
my set-up at the moment ....
about:addons Launcher, Fast Dial, Autohide Bookmarks, Change colors of tabs not selected, (Theme): Foxdie, Tab bar buttons as Round Tabs, Search bar - Auto-size, Custom Colored Tabs. and a few other things, no doubt.