Update the visible-but-unfocused tab's page, styles, and scripts without ever pressing refresh.

updateElements.js

(function (document) {
    ArrayForEach = Array.prototype.forEach || function (callback, scope) { for (var i = 0, l = this.length; i < l; ++i) callback.call(scope, this[i], i, this); };

    function updateElements() {
        var skip = document.hidden || document.mozHidden || document.msHidden || document.oHidden || document.webkitHidden || !document.hasFocus || document.hasFocus();

        ArrayForEach.call(document.querySelectorAll("html,link[rel],script[src]"), function (element) {
            if (skip) {
                return;
            }

            var xhr = new XMLHttpRequest;

            xhr.onreadystatechange = function () {
                if (xhr.readyState <= 1) {
                    return;
                }

                xhr.lastModified = xhr.lastModified || +new Date(xhr.getResponseHeader("Last-Modified"));

                element.dataset.lastModified = element.dataset.lastModified || xhr.lastModified;

                if (xhr.lastModified <= element.dataset.lastModified) {
                    xhr.abort();
                    return;
                }

                if (xhr.readyState == 4 && xhr.status == 200) {
                    element.dataset.lastModified = xhr.lastModified;

                    if (element.nodeName == "HTML") {
                        document.open();
                        document.write(xhr.responseText);
                        document.close();

                        return skip = true;
                    }

                    for (var clone = document.createElement(element.nodeName), i = 0, attr; attr = element.attributes[i]; ++i) {
                        clone.setAttribute(attr.name, attr.value);
                    }

                    element.parentNode.replaceChild(clone, element);

                    element = clone;
                }
            };

            xhr.open('GET', element.href || element.src || window.location.pathname, true);
            xhr.send(null);
        });
    }

    setInterval(updateElements, 200); updateElements();
})(document);