That is something with the mibbit site's certificates. The only issue is that the cert is self signed, which shouldn't be a problem. Click the "I understand the risks" link that should be in the error message page, and then click "add exception" link that should be shown after. Give it time to load the certificate then click "store this certificate" (going from memory... this may not be the exact name of each link, but the general gist should be apparent.) This is going from memory with Firefox as the browser. Other browsers my have other ways of accepting the self signed cert.