Mozilla Firefox is an open source web browser. XULRunner provides the XUL Runtime environment for Mozilla Firefox. The RHSA-2011:1242 Firefox update rendered HTTPS certificates signed by a certain Certificate Authority as untrusted, but made an exception for a select few. This update removes that exception, rendering every HTTPS certificate signed by that CA as untrusted. All Firefox users should upgrade to these updated packages, which contain Firefox version 3.6.22. After installing the update, Firefox must be restarted for the changes to take effect.