Seems promising, but in reality it’s not so great. I tried using it in conjunction with Simple Tab Groups and found that after changing to another group and coming back it had spontaneously created its own sub-tree group of (presumably) all unloaded tabs. It’s not clear how you can even undo this short of closing all the tabs it contains. Extensions shouldn’t do unexpected things like this. It also seems fairly CPU and memory intensive at times.

Another problem is that it doesn’t seem possible to organise open tabs (through drag and drop) without loading each individual tab. This makes it pretty useless as a utility for organising already open tabs.

F1 is a terrible choice for a shortcut.

If you use it from an empty Firefox, it will probably work as advertised, dutifully creating trees, etc. But if you already have lots of tabs open that you want to organise, this will do little for you.