The Internationalized Domain Name (IDN) display algorithm in Mozilla Firefox before 22.0 does not properly handle the .com, .name, and .net top-level domains, which allows remote attackers to spoof the address bar via unspecified homograph characters.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A17296
https://bugzilla.mozilla.org/show_bug.cgi?id=840882
http://www.ubuntu.com/usn/USN-1890-1
http://www.mozilla.org/security/announce/2013/mfsa2013-61.html
http://lists.opensuse.org/opensuse-security-announce/2013-07/msg00005.html