CVE 2006-0299
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.
See the 
CVE page on Mitre.org
for more details.
