Since the game was hacked you have to go to the tab that is called play game and you log in, then after you log in to the page you keep it open and then go on feralheart, and it will work.
Talking about the hack shouldn't really be mentioned in the forums ( if memory serves me right ).
But yes, as they two helpful floofens mentioned, trying out the new login system should work. Make sure you keep the tab up and running and make sure don't minimize it during your play.
Another thing , from what I've heard , the latest version of mac doesn't run Feral Heart so good. So in case nothing works, then this could also be the case and you would have to convert the Mac to its old settings. Hope it works out for you. ^^