This is where it's at, if you need tab groups for Firefox. The other extensions are too odd and obtuse for me, and this replicates Chrome-like grouping.

Closest tab grouping I've found compared to Edge's "tab islands." Having tabs grouped and hidden but leaving behind a group tab is very helpful. Thank you!

A way to keep tab groups across browsing sessions (after browser restart) is needed.

Colored grouping was mentioned before and would help with visual organization. I'd also take colored/unique tab group favicons to more easily see the difference between my groups.

The ability to keep a tab group expanded when none of the tabs are active would help if/when group coloring exists so that all website titles and favicons can remain visible yet clearly grouped.

Very good extension. Things missing off the top of my head are tabs being grouped by color and a way to backup or keep them consistent across devices.

If you're looking for a direct alternative to the way chrome groups tabs, this is it. I'm not joking, I looked for 3 hours. There are definitely improvements that could be made to the appearance of it all but the pure functionality outweighs that.