Web Designer I'm working with signed up a new client that needed an SSL certificate. We went to namecheap.com and purchased on from Comodo. Got all the needed files and set it up in ISPConfig.

To test we used Windows 7 running IE8, Firefox 3.6, and Chrome 12, and then on OSX with Firefox 4, Safari 5, and Chrome 13. All of them worked fine.

The client is getting 'This connection is untrusted' in Firefox 4 and 5. Safari works fine on their machine. On my machines and the designer's machines all works with no errors. I had the client forward me the info for the certificate that Firefox has and the fingerprints match up.

I have an old Windows 2000 VM with IE6 and Chrome and those work just fine as well.

Any ideas on what else to check or do?

The server is running Debian 5.0, up-to-date, with Apache 2 and ISPConfig 3.3