See this:
http://kb.mozillazine.org/Background_music_does_not_play

That web page tries to play a midi file (town2.mid) via BGSOUND.
If a website uses BGSOUND then it will only work in IE.
BGSOUND is not compatible with other browsers like Firefox.

I really can't be bothered waiting for ever for FF 4 people to fix the crashing Quicktime problem. Who ever heard of a browser not being able to play embedded midi music? I tried to associate other players, but FF 4 won't have it! What hold has Quicktime got over Mozilla, now?

You should be able to play midi files with the Windows Media Player if you use a MIME type that the WMP plugin supports like type="application/x-mplayer2"