Issue Firefox - Carousel Bootstrap with background-attachment: fixed - firefox

Question

I have an Issue with the Bootstrap Carousel.
I want to have the fixed effect but in Firefox it's giving jumps.
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;
}
You can try it hier:
https://codepen.io/TamZam/pen/ZvQvox
Any ideas why it happens?
Thanks!