Boxes Behind Letters in Java Games

We have two computers a MacBook and MacBookPro. Both were recently upgraded to Leopard. After the upgrade some Java games do not show some graphics the same way. The first picture, from the MacBookPro, shows the proper way the graphics should display. The second picture, from the MacBook, show the problems - little black boxes behind the letters.

Does anyone know if there is a setting I have missed to have both computers show the same. This happens in Safari and Firefox.

Thanks in advance for your help.