source: https://www.securityfocus.com/bid/45353/info

Mozilla Firefox, SeaMonkey, and Thunderbird are prone to multiple HTML-injection vulnerabilities.

Successful exploits will allow attacker-supplied HTML and script code to run in the context of the affected browser, potentially allowing the attacker to steal cookie-based authentication credentials or to control how the site is rendered to the user. Other attacks are also possible.

This issue is fixed in:

Firefox 3.6.13
Firefox 3.5.16
SeaMonkey 2.0.11

x-mac-farsi exploit: <meta charset="x-mac-farsi">?script ?alert(1)//?/script ?