gistfile1.js

(function() {
    function action() {
        // Whatever you want to do.
        alert("came back");
    }

    // In case the page gets reloaded upon coming back.
    if (/#redirected$/.test(location.href)) {
        action();
        return;
    }

    window.onload = function() {
        var a = document.body.appendChild(document.createElement("a"));
        a.href = "http://example.com"; // Wherever you want to go.

        location = location.href + "#redirected";

        // Needs to fire just after the window has finished loading, or the
        // original page will not remain in history.
        setTimeout(function() {
            try {
                // This works in webkit.
                var e = document.createEvent("MouseEvent");
                e.initMouseEvent("click", true, true);
                a.dispatchEvent(e);
            } catch (x) {
                // This works in Firefox.
                location.assign(a.href);
            }
        }, 10);
    };

    // We rely on this interval not firing before the window unloads.
    window.onunload = function() {
        var interval = setInterval(function() {
            if (/#redirected$/.test(location.href)) {
                clearInterval(interval);
                action();
            }
        }, 10);
    };
})();