Mozilla Thunderbird is a standalone mail and newsgroup client. The RHSA-2011:1243 Thunderbird 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 Thunderbird users should upgrade to this updated package, which resolves this issue. All running instances of Thunderbird must be restarted for the update to take effect.