I've had this issue as well. I believe the fix that worked for me was adding the following to the main .html file:
<script src="mygamesource.nocache.js"></script>
<!-- right below your nocache script -->
<script>
function handleMouseDown(evt) {
window.focus();
evt.preventDefault();
evt.stopPropagation();
evt.target.style.cursor = 'default';
}
document.getElementById('body').addEventListener('mousedown', handleMouseDown, false);
</script>
Credit to this post if it works for you.