The E4X implementation in Mozilla Firefox before 1.5.0.1, Thunderbird 1.5 if running Javascript in mail, and SeaMonkey before 1.0 exposes the internal "AnyName" object to external interfaces, which allows multiple cooperating domains to exchange information in violation of the same origin restrictions.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A1625
https://exchange.xforce.ibmcloud.com/vulnerabilities/24437
https://bugzilla.mozilla.org/show_bug.cgi?id=322312
http://www.vupen.com/english/advisories/2006/3749
http://www.vupen.com/english/advisories/2006/0413
http://www.securityfocus.com/bid/16476
http://www.securityfocus.com/archive/1/446657/100/200/threaded
http://www.mozilla.org/security/announce/2006/mfsa2006-08.html
http://securitytracker.com/id?1015570
http://secunia.com/advisories/22065