Supporting Background Size Cover and image position Fixed at the same time

.main-about-us {
  position: relative;
  width:100%;
  height:auto;
  min-height:31.25em;
  color:#fff;
  /*background:url(images/allaboutyou.jpg);*/
/*  background:url(images/about-image.jpg);
  background-size:cover;
  background-position:center center;*/
  background: url('images/about-image.jpg') center 0 no-repeat fixed;
  text-align:left;
  background-size: cover;
  transition: min-height .3s ease;
}