Use-after-free vulnerability in the nsINode::ReplaceOrInsertBefore function in Mozilla Firefox 4.x through 12.0, Firefox ESR 10.x before 10.0.5, Thunderbird 5.0 through 12.0, Thunderbird ESR 10.x before 10.0.5, and SeaMonkey before 2.10 might allow remote attackers to execute arbitrary code via document changes involving replacement or insertion of a node.