Unfortunately I'm not very familiar with how to fix this on mac, I'm a complete mac noob. I'm sure Nate or another more mac savvy person can help you out. With that said, this is something that will be fixed as soon as the new launcher is released, just a few more fixes and then we will have it out, hopefully within the next couple of days.

This will possibly help. http://support.apple.com/kb/PH14369

You need to go to System Preferences to change this. See the following website for more information: https://kb.wisc.edu/helpdesk/page.php?id=25443

Just right-clicking and selecting "Open" does the trick as well. No need to change any settings.