Can this poll be considered official ? I clicked the link and it looks like a Twitter poll or something.
Because of the fact that UltimaDark is going the hardest route, using a totally different API, unlike Dark Reader
It does, enable Desktop Mode and install
Yep, waiting for this feature so userChrome.js cook-ers can turn it into Tree Style Tab Group like Sidebery, with this config exposed it would be surprised if it takes long for us users to try the test version.
Smart Tab Group is pretty hype too.
Go to about:config and type groups, it's being actively developed.
There's also another API that you can actually use if you're a developer in Browser Toolbox, enable Browser Toolbox
and type gBrowser.addTabGroup, you can add tabs to group using this API, and if you find a way to append it to Tab Tray you should be able to create something like this image:
Yep, people have benchmarked:
There's many users who would kill to have this feature from Arc, just let you know. It's innovative, that's why it should be an option for people who want it, it needs to be polished though, like not popping on no audio videos and a soft-whitelist.