Does what it says on the box. Not buggy even though it's in active development. I'm running the fully enabled Nightly version, and it's a great replacement for Tab Groups. Not quite as user friendly but it's manageable. I would love the ability to move multiple tabs at once to a different container/group without having to switch to that new group immediately. Starting off trying to organize a couple hundred tabs initially lumped in default is quite a task when it has to be done one by one with 5 clicks each, but once that's over with it's not bad except for the odd time I forget to switch groups before opening more tabs then I have to move a few over at once. Functioning keyboard shortcuts would also be nice, I would prefer that to the big GUI organization screen that the old tab groups had. Another thing is I'd like the private tabs container to not be visible on the container selection interface by default, I don't use it and I don't appreciate people looking at my screen being able to see that and assume that I often do. Overall: good shit, keep it coming.

Edit in 2019-05: Also when there's more than 11 tab groups (including 'default') you have to scroll down to see the last one, the tab group selector window doesn't just get longer, which is kinda annoying, it looks like it should be able to hold 4 more within the length of the firefox window if the menu was as long as that. I'm using a standard 1920x1080 screen