There's a button next to "gyro" labeled "hands." Click on it, and the browser will ask for the camera permission. For me (Chrome, mac), I had to click on the

There's a button next to "gyro" labeled "hands." Click on it, and the browser will ask for the camera permission. For me (Chrome, mac), I had to click on the "cal" button next to it the first time to actually switch to the camera.