My new goto tool is TabSessionManager. It will sync your tabs automatically periodically to your Google account, and works on both Firefox and Chrome.
https://tab-session-manager.sienori.com/
I have used OneTab import/export when migrating, because BetterOneTab's sync is no longer supported. Toby doesnt allow saving of multiple tabs at once. OneTabPlus doenst have syncing and the backup function may be difficult after crashing because of the merged extensions storage in Firefox. Similar problems with TidyTab. save tabs to bookmark folder extension is very useful.
I'm no longer going to use OneTab because of the difficulty of manually restoring from a file in Firefox. The extension storage file has been converted to a Firefox db file. Supposedly it can still be done in Chrome. This problem is so bad, it looks like a paid extension has cropped up.
Using TSM above in combination with the TabMover Firefox extension is working, as it moves multiple tabs to a window, and I can close it to save memory. Then reopen it to add more tabs, and I dont think the other tabs are loaded. If they are there are extensions or even FF prefs to do that. Chrome has a move to specific window function by default.