But you can use `none`, at least according to: https://developer.mozilla.org/en-US/docs/Web/CSS/cursor.
Without it, I'm not sure how we are going to be able to hide the cursor.

Besides, we actually already use `cursor: none;` in the CSS, for example: https://github.com/mozilla/pdf.js/blob/master/web/viewer.css#L75. This was added in PR #2217.