google-header.user.js

// ==UserScript==
// @name        Google Header
// @namespace   http://kbinani.info/
// @description 
// @include     https://mail.google.com/*
// @include     https://www.google.com/reader/*
// ==/UserScript==

(function() {
  setInterval(function() {
    var list = document.getElementsByTagName("a");
    for (var i = 0; i < list.length; i++) {
      var anchor = list.item(i);
      if ("リーダー" === anchor.innerText
        || "Gmail" === anchor.innerText) {
        anchor.removeAttribute("target");
      }
    }
  }, 200);
})();