Reload web page(s) and bypass the cache. * Press and hold Shift and left-click the Reload button. * Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux) * Press "Cmd + Shift + R" (MAC) ----- Clear the cache and the cookies from sites that cause problems. "Clear the Cache": * Firefox > Preferences > Advanced > Network > Offline Storage (Cache): "Clear Now" "Remove Cookies" from sites causing problems: * Firefox > Preferences > Privacy > Cookies: "Show Cookies" ---- 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 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