Use-after-free vulnerability in the imgRequest::OnStopFrame function in Mozilla Firefox before 18.0, Firefox ESR 10.x before 10.0.12 and 17.x before 17.0.1, Thunderbird before 17.0.2, Thunderbird ESR 10.x before 10.0.12 and 17.x before 17.0.1, and SeaMonkey before 2.15 allows remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption) via unspecified vectors.