You will need to download and install Apple's QuickTime browser plugin in order to play MIDI files.

For more information about MIDI files, you may want to take a look at this Wikipedia article.

I hope that this is the information that you require. Please let us know.

Note that the QuickTime plugin shows in the System Detail list next to your question.

The QuickTime Plugin allows you to view a wide variety of multimedia content in Web pages. For more information, visit the QuickTime Web site.

Did you check in the QT setting if MIDI files are handled by QT?

• https://support.mozilla.org/kb/Using+the+QuickTime+plugin+with+Firefox