According to your system details, you posted your question using Firefox 14.0.1, so I assume Firefox starts ok; you just got that error message?

There is a malicious extension called XULRunner 1.9.1. Maybe that's what is giving you the error. If that's it, go to Firefox > Add-ons > Extensions, and beside XULRunner, click Remove.

See:

• http://kb.mozillazine.org/Browser_will_not_start_up#XULRunner_error_after_an_update

This issue is usually caused because some files weren't updated properly by the updater.

Do a clean reinstall and delete the Firefox program folder (C:\Program Files\Mozilla Firefox\) before reinstalling a fresh copy of Firefox.

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 14.0.x: http://www.mozilla.org/en-US/firefox/all.html

Uninstall your current Firefox version, if possible.

• Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other profile data are stored in the Firefox Profile Folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

No, Firefox v14 won't even start.

Tried the clean install as suggested but still Firefox 14 will not run and the same error message comes up

You did delete the entire Firefox program folder (especially application.ini)?

• http://kb.mozillazine.org/Installation_directory
• C:\Program Files (x86)\Mozilla Firefox\

Which security software (firewall, anti-virus) do you have?

Yes, deleted the Mozilla Folders completely.

Zonealarm Extreme Security.

If you use ZoneAlarm Extreme Security then disable Virtualization and reinstall Firefox. Other security software may have similar features to prevent Firefox from updating files properly.

• [/questions/880050]

Thanks for the help. Disabling virtualization of Zonealarm was the answer.

You're welcome