I have been looking for a way to make sure my web server is secure against a man in the middle attack. It does seem that Google Chrome and Firefox work in blocking requests to my server even if I select to advance after the security warning. I am testing this by using Charles Proxy to intercept Https traffic without having trusted the Charles Cert on my Mac.
When I run the same tests with Safari it will let me through if I chose to ignore the secure warning, which I expect a certain number of users to do. So it seems there is more configuration needed to lock down Safari traffic. I know this is possible because when trying to navigate to github.com with the same scenario I get the following message:
Does anyone know what GitHub is doing to block Safari traffic on an untrusted connection?