Firefox 3 SSL certificate warnings

So, I would just do what other people have suggested, which is, make no UI changes (no padlock, yellow or green bar, etc) for self-signed https, pretty much like with plain http; but store the cert the first time you connect. If the cert changed on a later visit, raise the alarm bells.

While it still wouldn't provide perfect security (especially if it's the first time you connect) - the point is to:
1) not give the illusion of security (same as plain http)
2) provide some protection against casual sniffing
3) provide some detection of MITM attacks (providing it's not the first visit)