As of October 2013, sound only works in Firefox and not in Chrome/Chromium. Emulation speed in Firefox is better than in Chrome, presumably because Firefox has better support for Emscripten's asm.js-based JS code. Internet Explorer 10 was supposedly supported very well by earlier versions of JSMESS with up to [https://github.com/jsmess/jsmess/wiki/Status 100% emulation performance] (including working sound) but the current JSMESS exits with an Emscripten error in IE 10.
The joystick is mapped to Alt and the arrow keys by default. The development version of JSMESS at archive.org also has support for USB gamepads but no sound.
==Usage on web pages and CPC6128 demo page==