Mozilla Firefox, possibly before 3.6, allows remote attackers to discover a redirect's target URL, for the session of a specific user of a web site, by placing the site's URL in the HREF attribute of a stylesheet LINK element, and then reading the document.styleSheets[0].href property value, related to an IFRAME element.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A12665
http://lists.fedoraproject.org/pipermail/package-announce/2010-May/041436.html
http://lists.fedoraproject.org/pipermail/package-announce/2010-May/041432.html
http://lists.fedoraproject.org/pipermail/package-announce/2010-May/041383.html