Mozilla Firefox 1.5.x before 1.5.0.12 and 2.x before 2.0.0.4, and SeaMonkey 1.0.9 and 1.1.2, allows remote attackers to bypass the same-origin policy and conduct cross-site scripting (XSS) and other attacks by using the addEventListener method to add an event listener for a site, which is executed in the context of that site.