Use-after-free vulnerability in the nsGlobalWindow::PageHidden function in Mozilla Firefox 4.x through 13.0, Firefox ESR 10.x before 10.0.6, Thunderbird 5.0 through 13.0, Thunderbird ESR 10.x before 10.0.6, and SeaMonkey before 2.11 might allow remote attackers to execute arbitrary code via vectors related to focused content.