The Firefox reason is because it needs the Flash to be able to play the MP3 format. While Firefox is an HTML5 browser, it supports the OGG format and has no native support for MP3. To use the HTML5 native support, you will need to supply the counterpart OGG format for each file. ie., A copy with a different encoding.
The Chrome problem is more surprising. My 1st thought that was the swfPath is incorrect, but since Firefox worked with Flash enabled, it would imply it is working.
I just reviewed on Chrome (win) and found no problem switching the Flash plugin off in about:plugins. Chrome can play MP3 files natively, so I used the jPlayer inspector to review which solution was being used.
iOS Safari has a problem with the media.duration being incorrect on the durationchange event when changing from 1 media to another. If I remember correctly, the 1st time it reports zero, the second time it reports the duration of the 1st song. There is a fix laid out and it will go into a patch. The solution will be along the lines of:
https://groups.google.com/d/topic/jplayer/MvPXJd0vl40/discussionI am not sure what the problem is with Chrome.
Have you tried on an old IE6 browser to see if there are any JavaScript errors?
If you review on Opera, its Dev tools tend to be pretty good. Opera should behave the same way as Firefox btw. It needs Flash to play MP3 format. All the dev tools are getting quite good now. Even IE9 beta dev tools were a pleasant surprise when I took a look at them. I tend to use Firebug mostly though.
It's a long shot, but is the mp3 mime type audio/mpeg ?
Best regards,
Mark P.