The normalizeDocument function in Mozilla Firefox before 3.5.12 and 3.6.x before 3.6.9, Thunderbird before 3.0.7 and 3.1.x before 3.1.3, and SeaMonkey before 2.0.7 does not properly handle the removal of DOM nodes during normalization, which might allow remote attackers to execute arbitrary code via vectors involving access to a deleted object.