Try following the instructions here: Firefox will not start

That can be a problem with the Norton toolbar (coFFPlgn.dll).

See Firefox 9 Support for Norton Toolbar:

• http://community.norton.com/t5/Norton-Internet-Security-Norton/Firefox-9-Support-for-Norton-Toolbar/td-p/615563

I am using McAfee Total Protection instead of Norton But the same issue. I can not start Firefox past version 9.

First of all you could try installing the latest version and see if that would fix the problem

Does Firefox crash (you get a Firefox has crash window) or does Firefox simply doesn't start?

See:

• http://kb.mozillazine.org/Firefox_crashes
• https://support.mozilla.org/kb/Firefox+crashes

A possible cause is security software (firewall,anti-virus) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/kb/Server+not+found
• https://support.mozilla.org/kb/Firewalls