Firefox-UI-Fix/src/utils/_moz_document.scss

@mixin moz-document($urlList...) {
  $result: ();
  @each $prefix, $urlPattern in $urlList {
    $result: append($result, #{$prefix}(if($urlPattern, "#{$urlPattern}", null)), $separator: comma);
  }

  @#{-moz-document} #{$result} {
    @content;
  }
}