It was put together with all free software: OfficeLibre for design, Audacity for audio, Aquamacs for coding and Mozilla for testing/debugging.
I tested it with Firefox, Chrome and Safari. It probably doesn't work with Internet Explorer because it uses Wave files for the sounds, which are originally a Microsoft standard, which is probably why it works with every browser except Microsoft's. If they are too lame to fix it, why should I even bother? Get yourself a real web browser.