I checked your file in beta R216.
You try to launch play right "On start of layout".
In my console, Firefox indicates this message :
La lecture automatique n’est autorisée que lorsqu’elle a été approuvée par l’utilisateur, que le site est activé par l’utilisateur, ou que le média est muet.
Auto playback is only authorised if it has been approved by a user, that the website is activated by the user, or that the media is muted.
As indicated in the Audio plugin manual article, browsers expect a user input before starting audio.
Music starts and plays as intended if I move the event from On start of layout to the second event "Touch: on tap gesture".