mozilla/pdf.js — pull request #958 by jviereck (2011-12-18 21:53:43+00:00)
Title: Render the next not yet visible page in the background

By rendering the next page in the background before the user scrolls to it, it looks like PDF.JS is "fast" enough to render the page just in time. Otherwise, the user sees how the page builds up in front of him.

This doesn't work if the user scrolls to fast, but from my experience this is still pritty good^^