Mozilla Firefox before 16.0 Firefox ESR 10.x before 10.0.8 Thunderbird before 16.0 Thunderbird ESR 10.x before 10.0.8 and SeaMonkey before 2.13 allow remote attackers to conduct cross-site scripting (XSS) attacks via a binary plugin that uses Object.defineProperty to shadow the top object and leverages the relationship between top.location and the location property.