* Type about:config into the location bar and press enter * Accept the warning message that appears, you will be taken to a list of preferences * Locate the preference browser.sessionstore.resume_session_once, if its value is set to true, double-click on it to change its value to false

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