Hello worf77bb, any luck if you delete in your profile folder the User.js file you have ?

The user.js file does not exist by default. If you create the file, forget it, if you have not create the file then delete the User.js file, to see if the problem goes away (some programs create and write in the file also).

thank you

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.

Make sure that you do not use "Use custom settings for history" to clear the "Browsing History" when you close Firefox because that prevails and prevents Firefox from opening tabs from the previous session.

• https://support.mozilla.org/kb/Clear+Recent+History

You can check for problems with the sessionstore.js file in the Firefox profile folder that store session data.

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

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost and you will have to recreate them (make a note or bookmark them if possible).