One function of certificates is to authenticate sites. The other, equally important function, is to encrypt the connection. For an application that needs the encryption but doesn't need the authentication (webmail within a corporate intranet is a perfect example) Firefox's policy is obviously flawed.

At the very least, the pop-up message needs to be rewritten, as it does not fully explain in non-technical language why it has blocked the page, what you can do to view the page anyway, and under what circumstances it's perfectly ok to view the page despite the warning. If Mozilla tech's goal is to "fully inform their 'customers'" they are doing a terrible job of it.