作者様ありがとうございます。中身はこうなっています
document.body.addEventListener("DOMNodeInserted", function(e) {
var element = e.target;
if (!element.className.match(/^entry/)) return;
var title = element.getElementsByTagName("h2")[0];
if (title.textContent.match(/^(PR:|AD:|\[PR\])/i)) {
element.style.height = 0;
var event = title.ownerDocument.createEvent("MouseEvents");
event.initMouseEvent("click", true, true,
title.ownerDocument.defaultView,
1, 0, 0, 0, 0,
false, false, false, false,
0, title);
title.dispatchEvent(event);
}
}, false);