var nastyGlobalVariable='';
[].forEach
        .call(
                document.querySelectorAll("tr.zA"),
                function(tr) {
                    var tit = tr.querySelector(".xW span")
                            .getAttribute("title")
                            .replace(/at\s+\d+:\d+.*/, '');
                    if (tit != nastyGlobalVariable) {
                        nastyGlobalVariable = tit;
                        tr.insertAdjacentHTML(
                                        'beforebegin',
                                        '<tr class=""><td style="width:2px;background:#ccc"></td><td colspan=7 align=center style="background:#ccc;font-size:12px;padding:2px">'
                                                + tit + '</td></tr>')
                    }
                });