SME server creates one certificate for one domain. Check the domain that Firefox says the cert is for, and you will probably find the end users are not using it.
For example, if your machine is called 'sme' on the domain 'example.com', then the *single* cert will match only the domain sme.example.com. If you try to access
https://www.example.com/ then the cert will be in error. The same problem occurs if accessing IMAPS, POPS or SMTPS using a domain other than that in the cert. For example, using mail.example.com would seem logical, but you get a cert error if the cert is actually registered against
www.example.com, so your e-mail client should use the less-intuitive
www.example.comWhat you probably need to do, is to create additional certs for each domain the users will be visiting.
There is a little bit about custom certs here:
http://wiki.contribs.org/Certificate but I've never seen a HOWTO on adding multiple certs.
I wonder if SME Server should be creating multiple self-signed certs by default, for a range of domains, www-, mail-, pop-, etc.?
Oh, and IE7? Completely unecessary scary-tactics, requiring five mouse clicks and ignoring of dire warnings to get around it. It's just silly, but I guess it was put in to help ease us into the wonderful world of Vista.