Works fine in Waterfox

Working fine in Firefox

It does, at least in theory. It displays the option to enable VR for me on Chrome for Android which pops you into Google Cardboard. I can look around fine but without a controller I don't think there's a way to move.

For Chrome on Windows, I had to enable "WebXR Incubations" (chrome://flags/#webxr-incubations), manually start Steam VR, then restart Chrome. The option to enable VR appears, but then in the headset it's just a white screen. Maybe I'm missing a step or maybe it's just broken.