Saw your post over in FF ... Welcome to the world of folding.
Do you have some more details ... Could you post the folding log file showing what system and configuration you run ? And what project you got assigned ?
You might have too much CPU allocated to the folding and run short of CPU power to drive the rendering; even with GPU. You could also try to change the rendering details as mention in FF.
Since Yosemite is still beta I have it only on a MBA where I don't bother with folding. So can't really test your setup. But I will try the viewer and see if I can reproduce.
And as you are brand new to folding: make sure to get a passkey installed as early as possible to receive so called "Quick Return Bonus" or "QRB". It require to finish 10 work units successfully and will then increase your points quite a bit.
http://folding.stanford.edu/home/faq/faq-passkey/
And don't forget to join team 3446, if you like.