// ==UserScript==
// @name          fullscreen
// @namespace     roger21.free.fr
// @icon          data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAAgAQAAAABbAUdZAAAALElEQVR42mP4DwQMaMQHg8P8EOLz%2F%2F%2FnIcR%2FOPEZpARGUEH2w2EefgiBxS0ARNpzyS9f0t0AAAAASUVORK5CYII%3D
// @include       *
// @grant         none
// ==/UserScript==

function exit_fs(e) {
  if(e.button === 1 && document.fullscreenElement !== null) {
    e.preventDefault();
    e.stopPropagation();
    document.exitFullscreen();
  }
}
document.addEventListener("mouseup", exit_fs, true);