How to properly write ScrollTop in FireFox?

Question

PHP

Hello!
This code works in google chrome:

$('div.full-text img').click(function() {
                var $loc = $(this).attr("src");
                $("#overlay_container img").attr("src", $loc);
                var $scrollnumber = $("body").scrollTop();
                $(".overlay").show().css('top', $scrollnumber-150);
                return false;
            });

How to rewrite or supplement this code to make it work in Mozilla?
Thank you.