An interesting idea that is similar to 'great suspender' for chrome, but it also had a bit more features like displaying the titles, session backups and so on. Anyway it's far better than most of alternatives for mozilla.
You might as well add some shortcuts if possible.

Love the speed and privacy protection in mind. I hope you can continue with the branch which you mentioned on github about idle pages etc and/or if you can add suspend all in this window etc will be great!

very cool! works fast, saves tabs. no privacy risks.Its free so big thanks to the dev!