Mozilla Firefox and Thunderbird 1.x before 1.5 and 1.0.x before 1.0.8, Mozilla Suite before 1.7.13, and SeaMonkey before 1.0 returns the Object class prototype instead of the global window object when (1) .valueOf.call or (2) .valueOf.apply are called without any arguments, which allows remote attackers to conduct cross-site scripting (XSS) attacks.