Technical issues---Sound

I am considering using MP3’s for an upcoming project.

I have always been able to play MP3’s …I cannot remember a time when I could not.

Does anyone know for sure if a plug in for MP3 is packaged with the newest browser updates?

The upcoming project must be playable across a network of computers without needing to download any plugins.

The end-user has the latest browser — but no access to download anything on the internet.

Thanks,
Janet