The layout engine in Mozilla Firefox 3.x before 3.0.5 and 2.x before 2.0.0.19, Thunderbird 2.x before 2.0.0.19, and SeaMonkey 1.x before 1.1.14 allows remote attackers to cause a denial of service (crash) and possibly trigger memory corruption via vectors related to (1) a reachable assertion or (2) an integer overflow.