If you have time I have made a new version of the game Stable 5 can you please re-test if you are now able to rotate your camera?
OK thank you for trying again. Did you walk forward? It should automatically capture the mouse on walking. Since this fix did not work for you. Can you tell me what Operating System and which browser you are using? I have tested the game on Firefox and Chrome. I have also seen reports of it working in Safari, though I can not yet confirm that.