With the latest release of Firefox version 59.0, we are not able to click on tiles in a tilelist and have them navigate to the specified NavigateURL.  We verified this even on the demo on the Telerik site:

https://demos.telerik.com/aspnet-ajax/tilelist/examples/overview/defaultcs.aspx

Workaround
<telerik:RadTileList RenderMode="Lightweight" runat="server" ID="RadTileList1" ScrollingMode="None" Width="640px"
 SelectionMode="Single" EnableDragAndDrop="true"></telerik:RadTileList>
<script>
    var $T = Telerik.Web.UI;
    $T.RadTileList.prototype._handleClickAfterDragging = function (draggable, args) {
        var tile = draggable.tile,
            shouldHandleClick = this.get_enableDragAndDrop() &&
                                !this._isTouchEvent(args._domEvent) &&
                                draggable._deltaX < 5 &&
                                draggable._deltaY < 5;
  
        if (shouldHandleClick) {
            tile.set_dragStarted(false);
            if (!$telerik.isMobileSafari) {
                tile._mouseClickHandler();
            }
            draggable._deltaY = 0;
            draggable._deltaX = 0;
        }
    }
</script>