Forgot about that, as I'm using Chromium 6 on a daily basis.
The author answered to some criticism: "It requires Chrome because the other browsers aren't fast enough yet. In some months hopefully it will run fast properly in all browsers (which is not exactly what happens with graphic cards requirements).
I've changed it so it uses an .ogg instead of an .mp3. Albeit much slower, it should now also run in Firefox and Opera."