nostr:npub1e7xjcrjvf4ntrvz7dgflf7yh90r2qmeeahz3a7358z7m67h6qu3sxlm97p 

Is this what you mean by collections?

https://support.mozilla.org/en-US/kb/how-use-collections-addonsmozillaorg

If so, unless I misunderstand it, it doesnt appear to have any relationship to tab groups (the ability to collapse similar tabs into one tab in the tab bar itself, rather than some other window or menu)