mozilla/pdf.js — pull request #4556 by p01 (2014-04-03 11:49:14+00:00)
Title: Use Opaque Canvas

This improves painting performance and text rendering quality in some browsers, without any measurable performance impact.

Scrolling through the TraceMonkey PDF, several times, at three different zoom level with and without opaque Canvas, the average time to draw a page was the same in both Firefox Aurora and Opera Developer.