Mac OS X won’t trust self-signed certificates sometimes, but you can override that:
- Find your certificate file (probably near your web server configuration).
- Open the “Keychain Access” app.
- Drag your certificate into the app.
- Go to the “Certificates” section.
- Find the certificate and double-click it.
- Expand the “trust” section.
- Set “When using this certificate” to “Always Trust”.