$(document).ready(function() {
    if (top.location != self.location) {       
        $("a").each(function() {
        var currentHref = $(this).attr("href");
            //don't append parameter if href is null or it contains javascript code.
            if (currentHref != undefined && currentHref.indexOf("javascript") == -1) {
                var checkQuestionMark = currentHref.indexOf("?");

                if (currentHref.indexOf("?") > -1) {

                    currentHref = currentHref + "&" + "preview=true";
                    $(this).attr('href', currentHref);
                }
                else {
                    currentHref = currentHref + "?" + "preview=true";
                    $(this).attr('href', currentHref);

                }
            }
        });
    }
});