SlideUp("slow") and SlideDown("slow") happening instantly?

SlideUp("slow") and SlideDown("slow") happening instantly?

When using slideUp and slideDown I'm getting something that looks more like a hide/show in all browsers. Can't seem to figure out what I'm doing wrong. Here's the code I'm running. I tried to nuke the opacity stuff...but that doesn't seem to have any effect. Ideas?
  2. // script
  3. $('.head-menu-container').click(function () {
  4.       $('.menu-list-container').slideDown("slow");
  5. });

  7. // css and html
  8. .menu-list-container { display: none; background: #454545;  opacity: 0.8; filter: alpha(opacity=80); min-width: 272px;  min-height: 200px;  -webkit-border-radius: 2px; -moz-border-radius: 2px; border-radius: 2px; position: absolute; top: 32px; left: 0px; }
  9. <div class="menu-list-container"></div>