App (pinned) tabs and Tab Groups (Panorama) are stored as part of the session data in the sessionstore.js file in the Firefox profile folder.

You can make a backup copy of the sessionstore.js file to be able to restore those groups.

You can check if there is are numbered sessionstore-##.js files in the Firefox profile folder that might have the lost groups.

• Help > Troubleshooting Information > Profile Director: Show Folder (Linux: Open Director; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Multiple_profile_files_created

The following solution is more simple but the options might be greyed out or some of the tabs not restored. Try clicking the Firefox button and then going to 'History' (or just click 'History' if you don't have the Firefox button) and then try clicking one of the following until one works:

• 'Restore Previous Session'
• 'Recently Closed Windows' > 'Restore All Windows'
• 'Recently Closed Tabs' > 'Restore All Tabs'

If none of those work then you will probably have to follow cor-el's suggestion or click 'Show All History' and then for each page you want to open right-click and select 'Open in a New Tab' (or right-click then w).

Theres a picture of what I backed up before i tried turning the .bak files into .js . When I did that nothing worked. How exactly do I do this?

Also thank you both for the fast replies.

You can delete the sessionstore-1.js and sessionstore-2.js as those are quite old and probably no longer needed.

You should make a backup copy of the sessionstore.bak file as that file is large enough to have some of the lost data.
You can also backup the sessionstore.js file.
The sessionstore.bak file with the file date appended was created automatically following the most recent Firefox update.

The point is to rename a sessionstore like sessionstore.bak to sessionstore.js to make Firefox use this file to see if that restores lost tabs. Remember that you may have to check for History > Recently Closed Tabs/Windows