CVE 2013-6673
Mozilla Firefox before 26.0, Firefox ESR 24.x before 24.2, Thunderbird before 24.2, and SeaMonkey before 2.23 do not recognize a user's removal of trust from an EV X.509 certificate, which makes it easier for man-in-the-middle attackers to spoof SSL servers in opportunistic circumstances via a valid certificate that is unacceptable to the user.
See the 
CVE page on Mitre.org
for more details.
