--- a/layout/style/full-screen-override.css
+++ b/layout/style/full-screen-override.css
@@ -16,16 +16,17 @@
      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;
+  perspective: 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 {