It's not the expiry that's an issue. Firefox says:
"Websites prove their identity via certificates. Firefox does not trust this site because it uses a certificate that is not valid for www.mojeek.com. The certificate is only valid for the following names: dock.shp.mcafee.com, *.dock.shp.mcafee.com
Error code: SSL_ERROR_BAD_CERT_DOMAIN"
Could be caused by the extensive (68k lines) of blocking in my /etc/hosts file, I suppose.