The server at https://deepbit.net/ does not deliver the intermediary certificate of the CA "issuer=/C=US/O=GeoTrust Inc./OU=Domain Validated SSL/CN=GeoTrust DV SSL CA", therefore all browsers only trusting the GeoTrust root CA "GeoTrust Global CA" give a certificate warning (i.e. Iceweasel (Firefox) on Debian Wheezy).

Please fix the web server configuration to deliver the intermediary CA certificate together with the server certificate.

See also https://www.ssllabs.com/ssltest/analyze.html?d=deepbit.net for some ideas for improvement.