delete the localstore.rdf file in the firefox profile folder. * http://kb.mozillazine.org/Corrupt_localstore.rdf * [[Profiles - Where Firefox stores your bookmarks, passwords and other user data]]

This may be caused by the changes that Ubuntu makes. Start Firefox in <u>[[Safe Mode|Safe Mode]]</u> to check if one of the extensions (Firefox/Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Firefox/Tools > Add-ons > Appearance). *Do NOT click the Reset button on the Safe Mode start window. *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes Ubuntu 11.xx and later displays window menus in the control bar at the top of the screen with the switch to the Unity window manager. * http://en.wikipedia.org/wiki/Ubuntu_Unity