Mozilla Thunderbird is a standalone mail and newsgroup client. Several flaws were found in the processing of malformed HTML content. HTML containing malicious content could cause Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. Note: JavaScript support is disabled by default in Thunderbird. The above issues are not exploitable unless JavaScript is enabled. 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.