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 [2] and sessionstore.bak in the Firefox Profile Folder. * Help > Troubleshooting Information > Profile Directory: Open Containing Folder * http://kb.mozillazine.org/Profile_folder_-_Firefox 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 open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them). See also: * [1] http://kb.mozillazine.org/Session_Restore * [2] http://kb.mozillazine.org/sessionstore.js ---- See also: *http://kb.mozillazine.org/Firefox_crashes *https://support.mozilla.com/kb/Firefox+crashes