about:tabs

... which brings up a simple text listing, one URL per line, of all tabs you have open. This would allow you to quickly, easily, checkpoint (or, bookmark) your open tabs.

I, personally, and rsync.net as a firm have offered bounties for this simple feature for over ten years now. I think we offered up to $2k at one point ?

This doesn't need to be a plugin - it is so dead simple and so necessary that it should just be built in.