For Firefox Browser if you use a godaddy linux server, you must add a .htaccess file to the folder root that holds the ogg files with this code,
AddType application/ogg .ogg
otherwise you get the flashing player with no functionality and then you'll search like I did..."html5 audio tag not working in firefox"
FYI: You can use the FREE VLC Player to convert mp3 files to .ogg files. VLC PLAYER