Hey! So I finally felt inspire and made a demo of my Firefox userchrome.css and Tree Style Tabs customization and CSS on my Github here [1]. It makes it so that the Tree style tabs expand and contract over the page, showing just the favicon and number of sub-tabs when contracted, along with a few other things, like reducing border sizes and adding better indication for sound in a tab. It's pretty nifty I think; I hope someone finds it to their liking. :)

https://github.com/jessebeard/firefox_settings