this is probably one of the best extensions I've used, with features that are useful, obvious & intuitive right out of the box.
I have a few extensions that I install on every browser, and this will be one of them

多段タブがバージョンアップのたびに使えなくなるので見限り代替となるものを探していました。

please make it possible to hide the original firefox tabs

The number 1 reason why I use Firefox!

Es macht, was ich erwartet habe: ich kann Bookmarks hierarchisch sortieren.
Man kann immer etwas verbessern, ich gebe trotzdem 5 Sterne, weil ich es toll finde, wenn jemand etwas kostenlos programmiert.

Makes tabbing much easier and more user-friendly. Works exactly as stated. : )