Mozilla Firefox before 2.0.0.15, Thunderbird 2.0.0.14 and earlier, and SeaMonkey before 1.1.10 allow remote attackers to execute arbitrary code via an XUL document that includes a script from a chrome: URI that points to a fastload file, related to this file's "privilege level."

More... (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-2802)