Add current class to ancestor li elements prior to initialising Superfish

jQuery Superfish pathClass support

$(document).ready(function(){ 

    //this will be used more than once so save it to a variable
    var menu = $('ul.sf-menu')

    //given that you already seem to have the current page marked with 'current' on the relevant li,
    //find that li, then find any ancestors of it and add 'current' to them also
    menu.find('.current').parents('li').addClass('current');

    //once you have done that, then initialise Superfish
    menu.superfish({ 
        pathClass:  'current' 
    }); 

});