this is PUSHKA

I like it a lot better than Tree Style Tabs. Sidebery is the superior add-on.

It's under very active development and receives regular updates.

It's a real must-have in Firefox, and I think Mozilla should implement it as an official functionality.

This extension has matured a LOT! Extremely configurable. I've used Firefox with Tree style tab a lot in the past, then switched to edge for some time (once they added native side-tabs) and now floating between the 2 browsers. Been using visual tabs more recently to keep things simpler. Now trying Sidebery again & it's been a very nice UX, better then TST. Search tab feature is in v5 beta and that will probably round out what I need from this side tab type of extension :)

Extremely good work to update and maintain this actively for firefox which is right now an extremely good browser (even though missing side-tabs natively and we have to resort to custom overrides etc), thank you sir!

I have to use it longer but this may be even better than Tree-Style Tabs (which is very good, to be clear)

Replaces with benefits both Tree Style View and Simple Tab Groups. The first one still is great. The latter is very buggy. But Sidebery replaces both, with an smooth experience

This extension is the main reason why I give up on Chrome. Especial when Google closed a sync with Chromium.