Is Firefox creating a file sessionstore.js in the Firefox Profile Folder? * http://kb.mozillazine.org/Profile_folder_-_Firefox *http://kb.mozillazine.org/sessionstore.js 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.<br /> 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