The browser engine in Mozilla Firefox before 8.0 and Thunderbird before 8.0 does not properly allocate memory, which allows remote attackers to cause a denial of service (memory corruption and application crash) or possibly execute arbitrary code via unspecified vectors.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A14239
https://bugzilla.mozilla.org/show_bug.cgi?id=682727
http://www.mozilla.org/security/announce/2011/mfsa2011-48.html