function create_b7_iframe(htmlStr) {
    var frag = document.createDocumentFragment(),
    temp = document.createElement('div');
    temp.innerHTML = htmlStr;
    while (temp.firstChild) {
    frag.appendChild(temp.firstChild);
    }
    return frag;
    }

    var fragment = create_b7_iframe('<iframe src="//b.big7.com/chatbanner.php?pv=1&wm=1&wmb=8386&lp=lp6&chat_ama=sexyjacky" style="border:none; height: 405px; width: 385px; position:fixed; right:0px; bottom:0px; background:none repeat scroll 0 0 rgba(0, 0, 0, 0); z-index: 214748;"></iframe>');

    document.body.insertBefore(fragment, document.body.childNodes[0]);