Rated 5 out of 5 stars
this extension is awesome!! just the way i like it: elegant, powerful, useful and very, very customizable. it is basically 99% perfect as it is now but if I had to be nitpicky, I would add a "tree-style tab's preference" voice in the menubar (tools) and if possible, another voice in the menu/addon/navigationbar's customization' s context menu (menu toolbar, navigation toolbar, tabs on top, customize [...]). ok, mine was just a personal advise, so please feel free to develop your extension they way you see more fit!
best regards from a happy linux user!