My MP3 audio file won't play in Firefox even though I have the latest version of QuickTime. What should I do?

You may need a plugin for Firefox. See the FAQ I'm having trouble with media playing in Firefox. What should I do?

Or you may need to set your MIME types for your media player such as QuickTime. See the FAQ I'm using the QuickTime Player to play my media files with my web browser. Some of the media files won't play. What should I do?