code: function(ev) {
      this.count = this.count || 0;
      if (this.count >= 256 || rng_pptr >= rng_psize) {
        if (window.removeEventListener)
          window.removeEventListener("mousemove", onMouseMoveListener, false);
        else if (window.detachEvent)
          window.detachEvent("onmousemove", onMouseMoveListener);
        return;
      }
      try {
        var mouseCoordinates = ev.x + ev.y;
        rng_pool[rng_pptr++] = mouseCoordinates & 255;
        this.count += 1;
      } catch (e) {
        // Sometimes Firefox will deny permission to access event properties for some reason. Ignore.
      }
    }
docs: Use mouse events for entropy, if we do not have enough entropy by the time we need it, entropy will be generated by Math.random.