The API is called WebXR (
https://www.w3.org/TR/webxr/,
https://developer.mozilla.org/en-US/docs/Web/API/WebXR_Devic...). You can find a lot of "getting started" samples here (
https://immersive-web.github.io/webxr-samples/). Mozilla Hubs (
https://hubs.mozilla.com) is publicly available. Message me and I will show you what I'm making at work (it's not exactly hidden, but it's also only meant for our existing customers and I don't need the extra traffic from posting publicly).