The gPluginHandler.handleEvent function in the plugin handler in Mozilla
Firefox before 18.0, Firefox ESR 17.x before 17.0.2, Thunderbird before
17.0.2, Thunderbird ESR 17.x before 17.0.2, and SeaMonkey before 2.15 does
not properly enforce the Same Origin Policy, which allows remote attackers
to conduct clickjacking attacks via crafted JavaScript code that listens
for a mutation event.