There is some weirdness about the way Mudcat serves MIDI files - probably in the wrapper stuff that tells the receiving computer what to do with the file. They usually don't immediately play in the browser itself, though this browser is quite capable of playing MIDIs on other sites. (It's a bit reassuring to know they act weird on Windows machines too). I've always had to save them and then play them through a player application. That player application can be the browser itself, if I drag the file icon onto the running-applications menu. It's the launching process that doesn't work.