Don't accept any new certificates within browser, chat application or mail client.

That may not be enough, comodo has issued certificates without checking identity of servers for such as yahoo, google, etc.

It may be possible that some of these certificates are not revoked (detected) yet.

http://threatpost.com/en_us/blogs/ph...-others-032311

EDIT: Tribute to Comodo: https://bugzilla.mozilla.org/show_bug.cgi?id=647959