Integer overflow in an array class in Mozilla Firefox 3.5.x before 3.5.11 and 3.6.x before 3.6.7, Thunderbird 3.0.x before 3.0.6 and 3.1.x before 3.1.1, and SeaMonkey before 2.0.6 allows remote attackers to execute arbitrary code by placing many Cascading Style Sheets (CSS) values in an array, related to references to external font resources and an inconsistency between 16-bit and 32-bit integers.