It can also be enabled in Firefox Beta with "browser.tabs.groups.enabled" but it's still a bit buggy there. Ironically, Firefox was the first browser to have tab groups with Firefox 4 until they removed it because "nobody used it".
Tab Groups remains a good idea on paper but no one has done a useful implementation of it. I remember during the Firefox 4 Tab Group era I purposed that Tabs from site ( Say HN ) and any Tabs opened from that site, for example I have another tab from this submitted links bugzilla.mozilla.org. All To be moved together into a tab group instead of just moving site to a tab group.
It was rejected for whatever reason.
https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...
oh no. For some reason, the Microsoft's abortion makes tab groups when i move tabs, with no option to disable it.