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 do not properly restrict use of the type attribute of an OBJECT element to set a document's charset, which allows remote attackers to bypass cross-site scripting (XSS) protection mechanisms via UTF-7 encoding.