Mozilla Firefox 3.6.x, 3.5.x, 3.0.19, and earlier, and SeaMonkey, executes a mail application in situations where an IFRAME element has a mailto: URL in its SRC attribute, which allows remote attackers to cause a denial of service (excessive application launches) via an HTML document with many IFRAME elements.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A12386
http://www.securityfocus.com/archive/1/511327/100/0/threaded