Unfortunately, it's prevented from working in Firefox by Firefox's anti-default-audio feature. The trouble is, the thing creates an audio context on page load, not when you click the on button. Firefox won't let a page create an audio context without user interaction.

Very cool! This might be a good time to mention a JavaScript emulation I made of the EMS Synthi A, which was also present at the BBC Radiophonic Workshop (well, the closely-related EMS VCS3 was) and contributed, among other things, to some SFX for Doctor Who: https://github.com/AlexNisnevich/synthi-js

This was a project from 6-7 years ago and I had to rely on a third-party library for the web audio bits. If I re-did it today, I'd definitely do it all in native Web Audio.

Thanks for posting this. It's hard to navigate on my phone, so I'll just comment here to remind myself to visit later.

https://youtube.com/watch?v=jetzY-W78gg

First heard this a few years ago from a Delia Derbyshire biopic with Caroline Catz and Cosey Fanni Tutti.