If i go to a site that has an invalid security certificate, epiphany refuse to load the page and gives a secure connection failed page.

eg https://grid-voms.desy.de:8443/voms/ilc/

"Secure Connection Failed

grid-voms.desy.de:8443 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…"

clicking on the add exception link reveals
"You should not add an exception if you are using an internet connection that you do not trust completely or if you are not used to seeing a warning for this server.

If you still wish to add an exception for this site, you can do so in your advanced encryption settings."

There is no hint to where one might find the advanced encryption settings, and what option to change.

Firefox 3 gives a similar message, but has a button you can press to add the exception. This seem like the best solution to me.