Q: The browser tells me that an SSL certificate is untrusted.

Answer: To ensure that your certificate is trusted in all browsers, in addition to the certificate issued for your domain, you must also install the server root certificate of the certification center – Intermediate CA Certificates.

Download the root CA SSL certificate and detailed instructions on how to install, you can at the following links:

Geotrust Intermediate CAs

RapidSSL Intermediate CAs

Thawte Intermediate CAs

VeriSign Intermediate CAs