Safari is included on your mac, so give that one a try. FYI, Netscape doesn't really exist anymore, Firefox has taken its place.
Do you have any Firefox extensions installed? There could be a conflict that is affecting how PowerGallery looks. I use Firefox, Chrome, and Safari on my mac and all of them render PowerGallery like it should.
Can you also try going to the powergallery-demo.com site and see if that renders the same way for you?