I haven't seen an idea quite like this, and I believe it has the advantage of using a lot Firefox functionality already in place, so may be easy to implement.
I've usually got maybe 200 or 300 tabs open --- all the time --- though there are of course occasional additions, deletions, etc. And I always have Firefox restore them when I reboot. But they tend to be very disorganized. Here's a suggestion for enabling the organizing of them more easily and quickly, using several features already available in Firefox.
1) use ctrl-shift-d to create a set of bookmarks with all of the tabs
2) export this set of bookmarks as HTML to a file
3) use your favorite text or HTML editor to organize the tabs
4) import this organized file into Bookmarks (with the same or a different name)
5) allow Firefox to open this new bookmark file as a new set of tabs (possibly replacing some tabs currently in use)
This seems to me a very simple and logical (and possibly not too difficult to implement) method of organizing a set of disorganized tabs, using a lot of Firefox infrastructure already in place. It would be a big help to me, and I suspect many others as well.