gecko-dev/layout/style/full-screen-override.css

/* 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: initial !important;
  /* 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: initial !important;
  /* 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: initial !important;
  clip-path: initial !important;
  filter: initial !important;
  clip: initial !important;
  transform: initial !important;
  transform-style: initial !important;
  /* FIXME: do we need to worry about 'overflow'? */
}

/* XXXdholbert This '@supports' wrapper should be removed once we remove
   support for the pref 'layout.css.will-change.enabled'. (This CSS rule should
   then be merged with the main rule up above.)  */
@supports (will-change: initial) {
  *|*:-moz-full-screen-ancestor {
    will-change: initial !important;
  }
}