Actually, upon closer inspection, in Chrome it starts in a buggy state where the sound is enabled but the speaker icon (at the bottom of the page) is set to mute. In Firefox, the buggy state doesn't occur: it's initially muted and you have to click on the speaker icon to enable the sound.
Thanks - I was so busy looking at the mountains I didn't see the unmute button. Well worth a reload !
Works for me, but I think it was muted at first.
Audio not working here either, same FF version. It works with Chrome.