Rated 5 out of 5 stars
Tab Mix Plus provides a Session Manager that permits saving all Ffx windows that are opened for or in a particular Ffx user profile, as well as for saving only the tabs of an active Ffx window. TMP also provides a menu for opening closed tabs; and much more.
BUT, and as far as I'm aware for now, TMP's SM doesn't permit saving and accumulating more than two session files. Maybe it does and to cause it to do this requires using the SM menu in the Ffx Tools menu, instead of only saving to save a session when Ffx is being closed. While I've been using TMP's session saver instead of Ffx's since having installed TMP, I've only been doing session saves when closing down Ffx. That doesn't permit having more than two sessions saved and if I'm not mistaken, then there are only two to choose from when there's been a Ffx crash. Perhaps using TMP's SM in the Tools menu does permit saving more session files for the user to be able to select from more than only two when starting up Ffx, but I'll have to try this out to find out.
Re. Ffx crashes:
Restoring sessions from crashed Ffx sessions has been no problem for me ever since I switched from Ffx 2.20 to 3.3.
Based on the images provided in the install page for your Session Manager add-on, it looks very interesting and a must to try it. So I just installed it and will check it out.
Some of the images show that your add-on permit saving and accumulating as many sessions and windows as a user wishes and this is a feature that will be very useful to me. It's been often frustrating to be lacking this feature.
Great idea you had with this add-on and I see MOSTLY high ratings for it from users here. It's clearly a MUST TRY.
Because I haven't yet restarted Ffx and it'll take some days before I can give an actual rating, but MOST users have already given 5 of 5 stars, I'll give it 5 for now and will later lower this if there's cause for me to do so.