I'm going to go out on a limb and assume this extension must have pre-dated the firefox group feature, because it's essentially an extension that does something firefox already has built in.

You simply select one or more tabs, right click, "add to group", have several groups if you so please, then when you want to leave the group/s of tabs to return to later, just right click and select "save and close group", and voilà. You can find you saved groups in the tab drop-down, NOT the bookmarks drop-down. Don't know if its universally displayed as such across devices but on my linux desktop it is the drop-down at the top right, 4th button from the right edge. Looky like-an upside-down ^ - i honestly dont know where that symbol is on the keyboard lmao.

In my opinion, when features are added that defeats the purpose of an extension, or a large chunk of an entire category of extensions, the developers should remove their extensions to help clean up the extensions hub, reduce confusion amongst the easily-confused, and realise they ought to stop beating a dead horse, el chapo.

But thats just my two cents, and after all, what do i know, aside from everything?