The new unsigned SSL warnings are a massive overreaction - so much so that I think Mozilla must have a deal with some certificate root companies to match their Google deal.
For a great deal of what goes on over the internet unsigned SSL is just fine. You don't care who you are dealing with, you just care that no one else can listen in (and sometimes that it is the same guy as last time). You only need authentication for banking, shopping and a few other corner cases.
The problem with "not caring who you're dealing with", is that it raises the possibility that who you're actually dealing with is a man in the middle, who is snooping on your traffic. If you get warned that a certificate is self-signed or signed by an untrusted authority, then you either have to check the key fingerprint or take a chance. Not that I'm happy with firefox taking this choice away from you, mind.
For a great deal of what goes on over the internet unsigned SSL is just fine. You don't care who you are dealing with, you just care that no one else can listen in (and sometimes that it is the same guy as last time). You only need authentication for banking, shopping and a few other corner cases.