Mozilla Thunderbird is a standalone mail and newsgroup client. A flaw was found in the way Thunderbird handled certain add-ons. Malicious, remote content could cause an add-on to elevate its privileges, which could lead to arbitrary code execution with the privileges of the user running Thunderbird. A cross-site scripting flaw was found in the way Thunderbird handled certain multibyte character sets. Malicious, remote content could cause Thunderbird to run JavaScript code with the permissions of different remote content. A flaw was found in the way Thunderbird handled large JavaScript scripts. Malicious, remote content could cause Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. 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.