What does it mean that the certificate has expired?
Exactly what it says. When the SSL certificate for BC was created, it was set to expire on January 1, 2009; and since it is now after that day, and since they have not yet managed to create and install a new certificate, Firefox does the right thing and complains (and offers you to add a temporary or permanent exception). There already is a post about this️ ↗ on MBC.Is my connection still encrypted?
Yes. If you click on View Page Info|Security in Firefox's context menu, you should read (among other things): Connection Encrypted: High-grade Encryption (AES-256 256 bit).Our own certificate is set to expire in April 2013, btw.
Surf safe;)
NFiH