見た目を変え難い nsIAlertService の代用。xul ファイルいらず。

ore-ore-alert-service.js

let xml =
  <window id="twitt-popup"
        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
        xmlns:xhtml="http://www.w3.org/1999/xhtml"
        pack="start"
        ondblclick="window.close()">
  <box id="dialog" style="padding: 10px; border: 2px solid #7B969C;">
    <hbox align="center" pack="center">
      <image id="profile-image"/>
    </hbox>
    <vbox>
      <label id="screen-name" style="font-size: 20px; font-weight: bold;"/>
      <description id="text" style="font-size: 14px; max-width: 200px !important"/>
    </vbox>
  </box>
  <script type="application/javascript"><![CDATA[
    function set (name, attr, value)
      document.getElementById(name)[attr] = value;

    let opts = window.arguments[0];
    set('profile-image', 'src', 'http://snca.net/blogfiles/devcat-face-red-eye-animation-optimized.gif');
    set('screen-name', 'textContent', opts.screenName + opts.rand());
    set('text', 'textContent', opts.text);

    // ちらっと左上に出るのを防止
    window.moveTo(-10000, -10000);

    let h = setInterval(function() {
      let x = screen.availLeft + screen.availWidth - window.outerWidth;
      let y = screen.availTop + screen.availHeight - window.outerHeight;
      window.moveTo(x, y);
      if (window.outerWidth > 100 && window.outerHeight > 100)
        clearInterval(h);
    }, 0);
  ]]></script>
  </window>;


function rand ()
  parseInt(Math.random() * 100, 10);

let uri = 'data:application/vnd.mozilla.xul+xml;base64,' + btoa(xmlst + xml.toString());

setTimeout(
  function(){
    let win =
      window.openDialog(
        uri,
        null, //'anekos-alert-window', // 指定すれば多重にポップアップしないかも
        'chrome,dialog=yes,titlebar=no,popup=yes',
        {
          screenName: 'anekos',
          text: '\u3075\u304A\u304A\u304A!!\n\u304A\u307E\u3048\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082\u3082 Vimperator \u4F7F\u3044\u306B\u3057\u3066\u3084\u308D\u3046\u304B\uFF01',
          rand: rand
        }
      );
    setTimeout(function() win.close(), 5000);
  },
  0
);


// chrome://global/content/alerts/alert.js
//view-source:chrome://global/content/alerts/alert.xul