Chrome and Firefox are showing error messages like this one and this one (sorry, both are in German). Safari just shows a blank page and I'm not able to open that specific web site although I'm sure that this site is not going to harm my computer or myself. For example this problem appears when I try to access my router at home or some other sites having problematic certificates - but they play fine when I'm at home.
Finally I found a solution for the problem.
Unfortunately there's neither a visible setting to set Chrome to warn me but allow the warning to be ignored, nor is that one in about:flags. But you can start Chrome with the flag
--ignore-certificate-errors
. That's not very comfortable but it works (last tested with Chrome 34).
Assuming Google Chrome is in your Applications folder, go to the Terminal and type following command:
/Applications/Google Chrome.app/Contents/MacOS/Google Chrome --ignore-certificate-errors &> /dev/null
That will open Chrome as usual but lets you browse any HTTPS site that has a problematic certificate and was blocked before.
I wouldn't do online banking this way; there I would be encouraged when Chrome tells me that there's something wrong with the site.
Maybe not many people will need this hint. I guess this problems only exist in rare circumstances with some proxy servers between your computer and the Internet.
[crarko adds: Yes, this probably is a rare case, although I've seen a lot of weird behavior out of Chrome lately. At first glance this sounded like a firewall/proxy config where the submitter worked, but that must not be where the proxy server is. I assume this only works for the specific session you launch using the command, but I'd make sure before using it. I don't use a proxy so I could not properly test this.]