> There's more to it than that -- Firefox and emscripten are tuned for > each other. Firefox has explicit optimization paths to handle > emscripten's output. Exactly. Firefox has optimized asm.js paths in its interpreter and asm.js is what emscripten outputs. For details, see http://arstechnica.com/information-technology/2013/05/native-level-performance-on-the-web-a-brief-examination-of-asm-js/3/