I assume this started recently after Firefox was operating normally for a while? In some cases, crashes shortly after startup can indicate a malware problem. You may want to run some supplemental scans. These two tools are highly regarded: Malwarebytes Anti-malware : http://www.malwarebytes.org/products/malwarebytes_free SUPERAntiSpyware : http://www.superantispyware.com/portablescanner.html If anything gets cleaned up from Firefox's program folder, you might want to reinstall Firefox 12 over your existing installation. You can get a fresh download at [http://www.mozilla.org/firefox/].

See also: *https://support.mozilla.org/kb/Firefox+crashes+when+you+open+it *https://support.mozilla.org/kb/Firefox+crashes *http://kb.mozillazine.org/Firefox_crashes