Great extension! I love being able to organize my tabs in this way, have been using this for a few years now.

Minor complaint:
The recent update that recently (I think?) introduced keyboard shortcuts that interfere with nominal text editing, e.g. Ctrl + Shift + Left/Right, which I use for highlighting words.
The keyboard shortcut editor is generally buggy, as I can't figure out how to disable a key; trying to set it to something useless, like Ctrl + Shift + / or pressing ESC, doesn't work; I can only sometimes set it to "undefined".

May just jump directly to wherever the config lives and kill the keys.

EDIT: Hup, it's already filed and fixed - awesome!
https://github.com/piroor/treestyletab/issues/1995

Switched back from chrome to firefox just to use this addon. Very valuable, great way to organize tabs for people like me, who have multiple sudden ideas scattered around and like to group those ideas in tree styled tabs. Too bad it's a bit glitchy lately - sometimes child tabs don't want to be attached to parent - for some reason they appear in different places, yet they seem to be still related. Reopening browser helps.

Thank you for this addon!

While this addon provides useful functionality, in its current state it is very buggy. I've had regular problems with tab positioning and movement, with child tabs being positioned outside of the area below the parent tab, and with the extension frequently preventing me from moving tab groups around in simple ways--being unable to reparent a tab and its children, or outright being unable to reorder top-level tabs. The functionality has been useful enough that I've worked around these problems instead of just uninstalling it, however now there is yet another problem with it. Now, the sidebar just perpetually shows a loading animation, never displaying the tabs for any of my windows. Closing and reopening the sidebar doesn't fix it. Disabling and re-enabling the addon doesn't fix it. Even uninstalling and reinstalling doesn't make it work again. As of now, all this does for me is take up a part of the side of my windows with a big blank area with a small animation in the middle of it. So, it's getting uninstalled. Hopefully this will be in a more usable state at some time in the future.

Neat design! Improves the Firefox user experience.

Thank you! I am happy each tree shares a root feature.