After many months of development, Firestorm released their viewer in a hurry because, i believe they wanted it to be available for the SL Birthday events. Performance and issues have been up and down during those months, and it appears Firestorm had some serious issues on Mac, at the very moment they released it. There is the gray texture issues, but also heavy fps drops for no reason after a moment of usage. Earlier versions were actually faster than this one on Mac, but also on Windows. I am certain things will get better and they must be working on a new update without the same pressure as they had when they released this one. We plan to share some of our discoveries regarding performance with LL, so eventually FS will benefit of some of those optimizations we have done on Megapahit (this will take a few weeks or months until it comes to them).