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.