I recently performed some cursory Javascript benchmarks with the new version of Firefox and Safari; curious about performance, I decided to do some testing of 32-bit browsers against their 64-bit counterparts. On Windows Vista x64, the only two browsers so available to me are Internet Explorer 7 and a recent nightly build of Firefox 3. The 64-bit comes from the Mozilla x86-64 project, specifically the build from 21 March 2008. The 32-bit build is a proper nightly from the same date from the official Mozilla FTP.
My hypothesis, before performing the tests, was that the 64-bit compilation would have little or no effect on the Javascript engine performance. It’s so difficult to optimize Javascript rendering, which is inherently single-threaded, and it seems likely to only benefit from a faster CPU clock than bigger memory registers. Afterward, I felt vindicated: Internet Explorer is likely the best test, and the difference was not statistically significant. In Firefox’s case, the 64-bit build was actually significantly worse, though this could easily be due to some other factor I have not taken into account; I have assumed that the source was compiled on the same date. See below for more details.
