I visited japan.indymedia.org and firefox gave me the "Invalid certificate" screen. I added an exception, but did not click "Store this exception permanently." But now firefox still happily visits the same site without giving any warnings, even after a restart of the browser. I tried going to the Options-Advanced-Encryption-View Certificates-Servers to remove the certificate but I did not find it there. How to remove this exception and make firefox give me the warning when visiting the site?