I'm a fan of tree-style tabs for firefox. Child descendants can be collapsed and you can re-arrange the hierarchy as you open/close tabs.

It's a little finicky with drag/drop but is very powerful.

Edge has vertical tabs which is space saving but lacks a hierarchy which is important to me.

I'd also be curious about the auto grouping.

I'm currently using Auto Tab Discard, which has a "Permanently delete (remove) old discarded tabs if they are inactive for (in hours)" and I'm manually grouping things with Panorama View. I don't know if it's built in to Firefox or one of the addons, but I've noticed it will already suggest an existing tab when I type the name/site in to the address bar.

Yeah, originally it did work on Firefox, but since migrating to manifest v3 and adding the tab grouping feature (API not available in Firefox), it is unfortunately no longer compatible. If I can in the future I'll definitely try to make something available for Firefox users.