Use-after-free vulnerability in the PresShell::DispatchSynthMouseMove function in Mozilla Firefox before 26.0, Firefox ESR 24.x before 24.2, Thunderbird before 24.2, and SeaMonkey before 2.23 allows remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption) via vectors involving synthetic mouse movement, related to the RestyleManager::GetHoverGeneration function.