CVE 2007-5947
The jar protocol handler in Mozilla Firefox before 2.0.0.10 and SeaMonkey before 1.1.7 retrieves the inner URL regardless of its MIME type, and considers HTML documents within a jar archive to have the same origin as the inner URL, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a jar: URI.
See the 
CVE page on Mitre.org
for more details.
