Rated 5 out of 5 stars
One of the biggest reasons I still use Firefox is this: Tabs in Chrome do not scroll. People tell me I should just learn to not open so many tabs. Those people can kindly get devoured by astral snakes.
This add-on takes tab functionality one step further, and while non-scrolling tabs are the reason I can't use Chrome, this add-on is now the reason why I specifically can't use anything other than Firefox. It's an excellent concept and improves my productivity immensely -- and saves some precious vertical real-estate.
The only real problem with this add-on is that dragging tabs from one spot to another, and particularly between different levels in the hierarchy, is somewhat laggy and unresponsive -- I hope this will be fixed soonish. Aside from that, and although it's somewhat difficult to get accustomed to at first, I strongly recommend this to anyone who, like me, opens loads of tabs and needs them organized EXACTLY HOW THEY NEED TO BE.