Firefox before 1.0.1 and Mozilla before 1.7.6 does not restrict xsl:include and xsl:import tags in XSLT stylesheets to the current domain, which allows remote attackers to determine the existence of files on the local system.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10682
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A100038
https://bugzilla.mozilla.org/show_bug.cgi?id=271209
http://www.securityfocus.com/bid/12659
http://www.redhat.com/support/errata/RHSA-2005-384.html
http://www.redhat.com/support/errata/RHSA-2005-176.html
http://www.mozilla.org/security/announce/mfsa2005-20.html