なんかやろうとしたけど...ダメだわ...こりゃ

gistfile11

function PB_RL() {
    setTimeout('PB_RL.readlater();', 1);
};

PB_RL.prototype = {

    readlater : function() {
        //PB_RL.u = encodeURIComponent(document.location.href);
        //PB_RL.t = encodeURIComponent(document.title.replace(/^\s\s*/, '').replace(/\s\s*$/, ''));
        //var url = 'https://pinboard.in/add?later=yes&noui=yes&jump=close&url='+PB_RL.u+'&title='+PB_RL.t;
        //var xhr = new XMLHttpRequest();
        //xhr.onreadystatechange = function() {
            //if (xhr.readyState == 4) {
                //var msg = (xhr.status == 200) ?
                    //"<p>Add Pinboard read later !</p>" :
                    //"<p>Add Pinboard failed(" + xhr.status + ")";
                //msg += '<p><a style="text-decoration:underline;cursor:pointer;" onclick="PB_RL.hideMessage()">[Close]</a>';
                //PB_RL.displayMessage(msg);
            //}
        //}
        //xhr.open('POST', url, true);
        //xhr.send(null); 
    },
    displayMessage : function(m, scale) {
        if (! this.msg) {
            this.msg = document.createElement('div');
        }

        var h = window.innerHeight ? window.innerHeight : document.documentElement.clientHeight ? document.documentElement.clientHeight : document.body.clientHeight;
                
        this.msg.style.cssText = 'display:block;position:absolute;margin:0px;padding:0px;font-size:18px;font-family:Arial;text-align:center;font-size:14px;font-weight:bold;color:#000000;background: #FFFFFF;border:1px solid #333333;z-index:100000;padding:25px';
        document.body.appendChild(this.msg);        
        this.msg.style.fontSize = scale ? (h * 0.06) + 'px' : '18px';
        this.msg.innerHTML = m;

        var y = window.pageYOffset ? window.pageYOffset : document.body.scrollLeft;
        var x = window.pageXOffset ? window.pageXOffset : document.body.scrollTop;
        var w = window.innerWidth ? window.innerWidth : document.documentElement.clientWidth ? document.documentElement.clientWidth : document.body.clientWidth;

        this.msg.style.top = ( y + ( h * 0.40 - this.msg.clientHeight / 2 ) ) + 'px';
        this.msg.style.left = ( x + ( w / 2 - this.msg.clientWidth / 2 ) ) + 'px';
    },
    hideMessage : function() {
        this.msg.style.display = 'none';
        this.msg = false;
    }
};

var PB_RL = new PB_RL();


void(0);

この方法だとどのみちHTML以外のリソース（画像など）で動かないので却下だわー。完全にムダだったわー。