For my own sites I use SSL certificates signed by my own CA
The CA certificate needs to be imported to the machines where I use the websites and for Mac OSX it needs to go into the system keychain - not the users keychain.
Importing via Keychain Access sometimes fails with cryptic error codes.
Here's how to do it via the command line:
sudo security import <cert file name> -k /Library/Keychains/System.keychain