Went to 8.40.4 (before 8.38.6) after trying out 8.42.3. It was nice, got to enable AIGLX (felt like Nvidia for a second), but that gave half the frame rates of glxgears 6000fps vs 11000fps with the current 8.40.4 driver.
So I'm back to 8.40.4, still running XGL and compiz that looks great, is fast, and firefox has no scrolling problems. Everything zippy as before. Well, the suspense of waiting for 8.42.3 was fun while it lasted.