firefox / thunderbird is vulnerable to arbitrary code execution. A web page containing malicious content could cause Firefox to crash or, potentially, execute arbitrary code with the privileges of the user running Firefox.
secunia.com/advisories/48972
secunia.com/advisories/49047
secunia.com/advisories/49055
www.mandriva.com/security/advisories?name=MDVSA-2012:066
www.mandriva.com/security/advisories?name=MDVSA-2012:081
www.mozilla.org/security/announce/2012/mfsa2012-22.html
www.mozilla.org/security/known-vulnerabilities/firefoxESR.html
www.securityfocus.com/bid/53220
access.redhat.com/errata/RHSA-2012:0515
access.redhat.com/security/updates/classification/#critical
bugzilla.mozilla.org/show_bug.cgi?id=738985
oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A16734