This is how GitHub's new AJAX file browser works.

github_tree_slider.js

GitHub.TreeSlider = function () {
    if (window.history && window.history.pushState) {
        function a() {
            if (e.sliding) {
                e.sliding = false;
                $(".frame-right").hide();
                $(".frame-loading:visible").removeClass("frame-loading")
            }
        }
        if (!($("#slider").length == 0 || !GitHub.shouldSlide)) if (!navigator.userAgent.match(/(iPod|iPhone|iPad)/)) {
            window.history.replaceState({
                path: this.pathFromURL(location.pathname)
            }, "");
            var e = this;
            $(".frames a.js-slide-to, .breadcrumb a").live("click", function (b) {
                if (b.which == 2 || b.metaKey || b.ctrlKey) return true;
                else {
                    e.clickHandler(b);
                    return false
                }
            });
            $(window).bind("popstate", function (b) {
                e.popStateHandler(b.originalEvent)
            });
            $(".frames .frame").live("webkitTransitionEnd", a).live("transitionend", a)
        }
    }
};