try Firefox instead of the native Safari browser

I am also using a mac, and TER chat didn't work in Safari but works perfectly fine in Chrome. If it still doesn't work, you could also try completely clearing out your cache and cookies.

It really is impossible to say what the problem is without more details. I'm not sure if TER provides technical support, but if they do, I'd suggest contacting them with the following info to make their job easier:
-your operating system
-the browser version you're using and whether the problem occurs in other browsers
-what extensions you have enabled, if any

Good luck!

Chat opens a new window so if you have pop-ups blocked it won't work.

You need to make sure you have the Flash plugin installed, since TER Chat uses Flash.

Chat works fine for me in Safari when I turn the popup blocker off. I even use it in "Privacy" mode.