Dunno how similar it is, but there is Simple Tab Groups: https://addons.mozilla.org/en-US/firefox/addon/simple-tab-groups/ https://addons.mozilla.org/en-US/fire

Dunno how similar it is, but there is Simple Tab Groups: https://addons.mozilla.org/en-US/firefox/addon/simple-tab-groups/ https://addons.mozilla.org/en-US/firefox/addon/simple-tab-gr... Also there's a bunch of userChrome css people have shared for Tree Style Tabs that makes the sidebar collapse and auto-expand on mouseover so it doesn't take much space. It's not part of the extension itself because they lost access back with the Firefox Quantum release and I guess no new API was ever made.