Or, what if the user's browser requested a site's public key on its first visit, but required it to be signed with a trusted CA? So to perform a MITM on an SSL connection, Mallory would have to both infiltrate a CA and MITM the user's connection on their first visit to a site.
When a site's certificate changes, Certificate Patrol shows you what has changed, including the public key fingerprint. So you easily detect the case when the site changes CA without changing their public key.
