Mozilla Thunderbird is a standalone mail and newsgroup client. Several flaws were found in the processing of malformed HTML content. Malicious HTML content could cause Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. A flaw was found in the way Thunderbird handled malformed JavaScript. Malicious content could cause Thunderbird to access already freed memory, causing Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. Note: This update disables support for Scalable Vector Graphics images in Thunderbird on Red Hat Enterprise Linux 5. All Thunderbird users should upgrade to this updated package, which resolves these issues. All running instances of Thunderbird must be restarted for the update to take effect.