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

// https://kittygiraudel.com/2013/08/08/advanced-sass-list-functions/
// https://gist.github.com/Jakobud/ec056b52f3673cc369dc97f2c2428424

@function remove($list, $value, $recursive: false) {
  $result: ();

  @for $i from 1 through length($list) {
    @if type-of(nth($list, $i)) == list and $recursive {
      $result: append($result, remove(nth($list, $i), $value, $recursive));
    } @else if nth($list, $i) != $value {
      $result: append($result, nth($list, $i));
    }
  }

  @return $result;
}

@function to-string($list, $glue: '', $is-nested: false) {
  $result: null;

  @for $i from 1 through length($list) {
    $e: nth($list, $i);

    @if type-of($e) == list {
      $result: $result#{to-string($e, $glue, true)};
    } @else {
      $result: if(
        $i != length($list) or $is-nested,
        $result#{$e}#{$glue},
        $result#{$e}
      );
    }
  }

  @return $result;
}