Firefox fullscreen video append DOM elements

Question

no matter how I put elements in DOM as an overlay on html5 video (statically or dynamically), those elements in Firefox are not visible, although the z-index is set to 2147483647, opacity 1 and display block.

See 2 similar answers, working in Chrome, but not in FF:

Overlay on HTML5 Fullscreen Video

Displaying elements other than fullscreen element (HTML5 fullscreen API)

Answer 1

To Display Overlay Element, instead of making video fullscreen, make parent of Video Element Fullscreen.

See Example Here - https://jsfiddle.net/tv1981/tm069z9c/128/

In following structure, I am making 'container' fullscreen

<div id="container">
  <div class="btn-fs" id="btnFS">
    Fullscreen
  </div>
  <div class='logo'>
    Logo Overlay
  </div>
  <video width="100%" height="100%" autoplay muted>
    <source src="https://file-examples-com.github.io/uploads/2017/04/file_example_MP4_480_1_5MG.mp4" type="video/mp4"> Your browser does not support the video tag.
  </video>
  <div class='footer'>
    This is Test Overlay for Video
  </div>
</div>

JavaScript

fs.addEventListener('click', goFullScreen);

function goFullScreen() {
  var fullscreenElement = document.fullscreenElement || document.mozFullScreenElement ||
    document.webkitFullscreenElement || document.msFullscreenElement;
  if (fullscreenElement) {
    exitFullscreen();
  } else {
    launchIntoFullscreen(document.getElementById('container'));
  }
}

This is working in Chrome Version 60.0.3112.101 (Official Build) (64-bit), FireFox Developer Edition 56.0b5 (64-bit)