It is possible that there is a problem with the files [http://kb.mozillazine.org/sessionstore.js sessionstore.js] and sessionstore.bak in the [http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder] Delete [http://kb.mozillazine.org/sessionstore.js sessionstore.js] and sessionstore.bak in the [http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder] * Help > Troubleshooting Information > Profile Directory: Open Containing Folder 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 to get lost, so you will have to create them again (make a note). See: * http://kb.mozillazine.org/Session_Restore

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