For what it's worth, this test has little to do with JS execution speed. See https://bugzilla.mozilla.org/show_bug.cgi?id=622358#c3 for an analysis of a profile of the test in Firefox. In brief, 80% is canvas operations due to the emulator making 1024 putImageData calls for every single frame. The time spent actually running JS is about 10% of the total time.