Are you running Firefox in full screen mode? Make sure that you do not run Firefox in full screen mode (press F11 or Fn + F11 to toggle; Mac: command+Shift+F). You can check: *http://kb.mozillazine.org/Corrupt_localstore.rdf You can also try to remove the Firefox plist file (org.mozilla.firefox.plist). * http://www.macfixit.com/article.php?story=20060606082246983 How .plist files become corrupt and troubleshooting the results Go to "Library > Preferences" and remove the plist file for Firefox (org.mozilla.firefox.plist).