I have a mac as well... I have never experienced these problems though. I'm guessing you have tried reinstalling it? What type of mac do you have, or how old?
hmm.... I also have a mac laptop. It is one of the newest versions though...Is their any particular time that it closes? Occasionally, mine closes when I scroll down too fast on the mods, or the replays list. Is it the same for you? Or just at random times?
What type of internet network are you on? At my school when I try to get on toribash, it freezes because of the school network airport that I am on, but when I get home, it works fine. Make sure your firewalls/airport isn't blocking anything.