Firefox prevents audio from playing with no initial user interaction like a play button. Can see the warning if you pop open the dev console. Don't know of workaround besides sites not creating an AudioContext on page load.
Edit: Keyboard input does not work :/ it was a good effort.
Found a workaround throw it in an iFrame and have the frame load with a user interaction. Here is a jsFiddle link, just click "Run" after the page loads.
You can explicitly allow it in Site Settings, and then reload the page. For me, I click the little button (looks like sliders) to the left of the URL, Site Settings, and then scroll down to change Site Audio to "Allow".
Found a workaround throw it in an iFrame and have the frame load with a user interaction. Here is a jsFiddle link, just click "Run" after the page loads.
https://jsfiddle.net/sg1r3h60/