jQuery UI Sortable: Firefox :active issue

Pseudo class :active gets suppressed by ui.sortable in Firefox

by TJ VanToll

HTML

<link href="http://code.jquery.com/ui/jquery-ui-git.css" rel="stylesheet">
<script src="http://code.jquery.com/jquery-git.js"></script>
<script src="http://code.jquery.com/ui/jquery-ui-git.js"></script>

<ul class="sortable">
    <li>Item 1</li>
    <li>Item 2</li>
    <li>Item 3</li>
    <li>Item 4</li>
</ul>

CSS

.sortable {
    list-style: none;
    padding: 0;
}
.sortable li {
    padding: 0.5em 1em;
    margin: 1em;
    border: thin solid black;
    cursor: pointer;
}
.ui-sortable-active {
    background: orange;
    cursor: move;
}

JavaScript

$.widget( "ui.sortable", $.ui.sortable, {
    _create: function() {
        this._super();
        this._on( this.element, {
            "mousedown > *": function( event ) {
                $( event.target ).addClass( "ui-sortable-active" );
            },
            "sortstop": function( event, ui ) {
                $( ui.item ).removeClass( "ui-sortable-active" );
            }
        });
    }
});

$( ".sortable" ).sortable();