Need Mac and Java Expert - My site works perfectly on PC's but is glitchy on FF and Safari

Hi, My site ([login to view URL]) works perfectly on PC's (with both IE and FF), but on Mac's everything becomes a little glitchy. In the FF browser everytime you go to the menu bar (tools, invite people,...) the board flickers. In Safari, no name transfers onto the board when you first log in. In order to understand the problem fully it is important to first test the site using a PC (invite yourself to a board if you have to), and then look at how things function on a Mac. If you have any questions let me know... Thanks, Jordan