I wanted to login to stackoverflow.com with my newly created Stack Exchange account. Unfortunately, it's not possible with Firefox on Mac OSX, because the four buttons on the login page below "Do you already have an account on one of these sites? Click the logo to log in with it here:" are not working. Clicking has no effect at all: not even throwing JS errors.
Maybe this could be a hint: When opening stackoverflow.com or meta.stackoverflow.com I always get the following log entry in the console:
[01:31:30.125] SecurityError: The operation is insecure. @ http://stackoverflow.com/:2879
It seems like other StackExchange sites aren't affected.
I'd really like to find a way to use Stack Overflow with Firefox.