It is possible that there is a problem with the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder.

Delete the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/sessionstore.js

If you see files sessionstore-##.js with a number in the left part of the name like sessionstore-1.js then delete those as well.
Deleting sessionstore.js will cause App Tabs and Tab Groups and all open tabs to get lost, so you will have to create them again (make a note or bookmark them).

See:

• http://kb.mozillazine.org/Session_Restore

Thanks but I've tried that fix numerous times. The sessionstore files just return and the problem never goes away.

Firefox should reopen windows if you delete the sessionstore.js files.

Do you have cleanup or security software that can cause problems with those files?