How to hide scrollbar in Firefox?

You can use the scrollbar-width rule. You can scrollbar-width: none; to hide the scrollbar in Firefox and still be able to scroll freely.

body {
   scrollbar-width: none;
}

To hide scroll bar on Chrome, Firefox and IE you can use this:

.hide-scrollbar
{
    overflow: auto;
    -ms-overflow-style: none; /* IE 11 */
    scrollbar-width: none; /* Firefox 64 */
}

I was able to hide the scrollbar but still be able to scroll with mouse wheel with this solution:

html {overflow: -moz-scrollbars-none;}

Download the plugin https://github.com/brandonaaron/jquery-mousewheel and include this function:

jQuery('html,body').bind('mousewheel', function(event) {
    event.preventDefault();
    var scrollTop = this.scrollTop;
    this.scrollTop = (scrollTop + ((event.deltaY * event.deltaFactor) * -1));
    //console.log(event.deltaY, event.deltaFactor, event.originalEvent.deltaMode, event.originalEvent.wheelDelta);
  });

This is what I needed to disable scrollbars while preserving scroll in Firefox, Chrome and Edge in :

          @-moz-document url-prefix() { /* Disable scrollbar Firefox */
            html{
              scrollbar-width: none;
            }
          }
          body {
            margin: 0; /* remove default margin */
            scrollbar-width: none; /* Also needed to disable scrollbar Firefox */
            -ms-overflow-style: none;  /* Disable scrollbar IE 10+ */
            overflow-y: scroll;
          }
          body::-webkit-scrollbar {
            width: 0px;
            background: transparent; /* Disable scrollbar Chrome/Safari/Webkit */
          }