New about:config settings for smooth scrolling.
It is just a very good suggestion: general.smoothScroll.mouseWheel.durationMaxMS 150 and general.smoothScroll.mouseWheel.durationMinMS 100 make FF's scrolling much better. With the default settings Firefox looks very laggy. It's very important to make browser's interface much smoother. I think this is the main case why Chrome has much more users now. This settings should have been changed just when Quantum was released to show more performance difference "before/after".