I haven't used this, as I didn't know it was a feature I needed until you mentioned it.
- https://addons.mozilla.org/en-US/firefox/addon/find-in-page-...
Tab Session Manager allows you to dump tabs to groups for restoration later, with auto-save at regular intervals. Works quite well!
- https://addons.mozilla.org/en-US/firefox/addon/tab-session-m...