144
You Can Now Try Firefox’s Vertical Tabs
(www.howtogeek.com)
A place to discuss the news and latest developments on the open-source browser Firefox
Oh, does this replace Tree Style Tabs?
Rather than replace, I'd guess it could be an alternative. The best part of it will be the ability to natively disable the top tab bar instead of needing a janky userchrome css hack that doesn't even fully work.