http://www.mozillazine.org/talkback.html?article=22211
and
http://www.mozillazine.org/talkback.html?article=22201

Description: Mozilla products, including the Firefox web browser and Thunderbird email application, contain a number of vulnerabilities. These vulnerabilities may allow an attacker to access your computer, run programs that could cause your computer to crash, or gain control of your computer. An attacker could exploit these vulnerabilities by convincing you to visit a web site or read an HTML formatted email message.

Solution: Upgrade to the latest versions of Firefox and Thunderbird. These vulnerabilities can be mitigated by disabling JavaScript. For more information about configuring Firefox, please see the Securing Your Web Browser document. Thunderbird disables JavaScript by default.