Can you try to start Firefox in Safe Mode to see if Firefox works properly with no error? You can start Firefox in Safe Mode below: *'''Windows/Mac''': Go to Help > Restart with add-ons disabled *'''Linux''': Run ''firefox -safe-mode'' in the Terminal/Konsole If Firefox opens up fine with no problems, it's probably one of your extensions that's causing the issue. You can re-enable your add-ons one by one until you find the one that causes the issue upon being re-enabled. ---- you can also check for problems caused by a corrupted localstore.rdf file *http://kb.mozillazine.org/Corrupt_localstore.rdf