If you use cleanup software like CCleaner then check the settings for the Firefox application. Using the "Show my windows and tabs from last time" setting is a more reliable way to restore session data. * [http://kb.mozillazine.org/Menu_differences Firefox/Tools > Options] > General > Startup: "When Firefox Starts": "Show my windows and tabs from last time" ---- It is possible that there is a problem with the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder. Delete the sessionstore.js [2] file and possible sessionstore-##.js [3] files with a number and sessionstore.bak in the Firefox Profile Folder. * Help > Troubleshooting Information > Profile Directory: Open Containing Folder * http://kb.mozillazine.org/Profile_folder_-_Firefox 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 * [3] http://kb.mozillazine.org/Multiple_profile_files_created

I had to set Firefox as my homepage. That seemed to work. Thank you all for your suggestions!