I find shadowmap calculations to be excruciatingly slow with Firefly, to the point that I often use raytraced shadows instead in my Firefly animations. This slowdown doesn't occur when I use the P4 renderer in Poser 5. Other than that, it's workable, as long as I don't use much dynamic hair (another big slowdown). I cranked out an 180-frame animation at 640x480 with dynamic cloth in about an hour this morning.