The Tor Browser / file revision

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 *|*:-moz-full-screen-ancestor {

   /* Ancestors of a full-screen element should not induce stacking contexts

      that would prevent the full-screen element from being on top. */

   z-index: auto;

   /* Ancestors of a full-screen element should not be partially transparent,

      since that would apply to the full-screen element and make the page visible

      behind it. It would also create a pseudo-stacking-context that would let content

      draw on top of the full-screen element. */

   opacity: 1;

   /* Ancestors of a full-screen element should not apply SVG masking, clipping, or

      filtering, since that would affect the full-screen element and create a pseudo-

      stacking context. */

   mask: none;

   clip: auto;

   filter: none;

   -moz-transform: none;

 }