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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:
Thanks for the tip! I'll give it a look and see if that fits my flow any better!
Naaaah it won't save you from your scattered X tabs... I'm in the exact same situation and it's mostly an organization problem or focus on a single task !
I somehow managed to get a bit better by simply to force myself to clean my whole browser before I shut down my PC.
That's basically my 'fix' too, I reboot the work computer at least once a week and close a ton of tabs on the personal computer whenever I notice I've got to scroll through all the tabs and can't find anything.