Firefox 3 and self-signed certificates

Firefox 3 displays a very different error message if it comes across a web page that has:

• an expired certificate
• a self-signed certificate (Examples: http://go.middlebury.edu/files or http://go.middlebury.edu/spam)

Here is a sample such message:

Secure Connection Failed
shark.middlebury.edu uses an invalid security certificate.
The certificate is not trusted because the issuer certificate is unknown.
(Error code: sec_error_unknown_issuer)
* This could be a problem with the server's configuration, 
  or it could be someone trying to impersonate the server.
* If you have connected to this server successfully in the past, 
  the error may be temporary, and you can try again later.

Or you can add an exception...

If you trust the website (if it is, for example, a Middlebury College site/page), you can safely use the "add an exception" option at the bottom:

• Click on the text "Or you can add an exception..."
• Click on "Add Exception"
• Click on "Get Certificate"
• Click on "Confirm Security Exception"

After this, Firefox will not display the scary error message.