jQuery(document).ready(function () {
    var $downsell = jQuery('div.element p').children('a'),
        $durl = $downsell.attr('href');//retrieve href from <div class="element"><p><a href="some-link"></a></p></div>
    var $address = window.location.href;//get url in window browser
    var $param = $address.replace('http://www.somedomain.com', '');//throw away the domain host
    if ($param != '') {
        $downsell.attr('href', $durl + $param);//combine the old link with the new one
    }
    console.log($param);//check the result using web developer console
});