Buffer overflow in the nsFloatManager::GetFlowArea function in Mozilla Firefox before 24.0, Firefox ESR 17.x before 17.0.9, Thunderbird before 24.0, Thunderbird ESR 17.x before 17.0.9, and SeaMonkey before 2.21 allows remote attackers to execute arbitrary code via crafted use of lists and floats within a multi-column layout.