Mozilla Firefox before 2.0.0.16 and 3.x before 3.0.1 Thunderbird before 2.0.0.16 and SeaMonkey before 1.1.11 use an incorrect integer data type as a CSS object reference counter in the CSSValue array (aka nsCSSValue:Array) data structure which allows remote attackers to execute arbitrary code via a large number of references to a common CSS object leading to a counter overflow and a free of in-use memory aka ZDI-CAN-349.