I glanced at your scroll.css and saw a bunch of rules that attempt to fiddle with the overflow/position attributes. This sort of thing confuses all browsers. Why not just use a normal scrollbar? It's fine to change the way it looks it if you want using the -webkit-scrollbar stuff you've done, but hacking out the normal web page scroll bar confuses everything. There are, for example, optimization opportunities in web rendering engines that only hit when the page is "normal" (which probably explains the poor performance other people are encountering).
(I noticed even on desktop Chrome the scrolling isn't smooth, unlike other pages. Probably for the same reason.)
