问题Firefox - Carousel Bootstrap with background-attachment：fixed

Question

我有Bootstrap Carousel的问题。

我想获得固定的效果，但在Firefox中它会跳跃。

HTML

<div id="carouselExampleIndicators" class="carousel slide" data-ride="carousel">
  <ol class="carousel-indicators">
    <li data-target="#carouselExampleIndicators" data-slide-to="0" class="active"></li>
    <li data-target="#carouselExampleIndicators" data-slide-to="1"></li>
    <li data-target="#carouselExampleIndicators" data-slide-to="2"></li>
  </ol>
  <div class="carousel-inner">
    <div class="carousel-item active">
      <div class="carousel-item-content" style="background:url('http://www.kia.ca/content/2018-soul/gallery/gallery-img-3.jpg')">
      </div>
    </div>
    <div class="carousel-item">
      <div class="carousel-item-content" style="background:url('http://carimages.silovendes.com/imgAutos/11/1056445-0.jpg')">
      </div>
    </div>
    <div class="carousel-item">
      <div class="carousel-item-content" style="background:url('https://kia.com.gt/images/modelos/rio/img/exterior-old//thumb/5.jpg')">
      </div>
    </div>
  </div>
  <a class="carousel-control-prev" href="#carouselExampleIndicators" role="button" data-slide="prev">
    <span class="carousel-control-prev-icon" aria-hidden="true"></span>
    <span class="sr-only">Previous</span>
  </a>
  <a class="carousel-control-next" href="#carouselExampleIndicators" role="button" data-slide="next">
    <span class="carousel-control-next-icon" aria-hidden="true"></span>
    <span class="sr-only">Next</span>
  </a>
</div>

CSS

.carousel-item {
  width: 100%;
  height: 100vh;
}

.carousel-item .carousel-item-content {
width: 100%;
height: 100%;
-webkit-background-size: cover !important;
-moz-background-size: cover !important;
-o-background-size: cover !important;
background-size: cover !important;
background-position: center center !important;
background-repeat: no-repeat !important;
overflow: hidden !important;
background-attachment: fixed !important;

}

你可以尝试一下：

https://codepen.io/TamZam/pen/ZvQvox

任何想法为什么会发生？

谢谢！