CVE 2006-4567
Mozilla Firefox before 1.5.0.7 and Thunderbird before 1.5.0.7 makes it easy for users to accept self-signed certificates for the auto-update mechanism, which might allow remote user-assisted attackers to use DNS spoofing to trick users into visiting a malicious site and accepting a malicious certificate for the Mozilla update site, which can then be used to install arbitrary code on the next update.
See the 
CVE page on Mitre.org
for more details.
