rtm_todays_task.user.js

// ==UserScript==
// @name           rtm_today's_task
// @namespace      http://d.hatena.ne.jp/samurai20000/
// @include        http://www.rememberthemilk.com/*
// ==/UserScript==

(function() {
     var contents = document.getElementById("content");
     if (contents) {
         var filter = document.getElementById("listFilter");
         var button = document.createElement("button");
         button.innerHTML = "today's tasks";
         button.addEventListener("click", function() {
             if (filter.value.indexOf("due: today") == -1) {
                 filter.value = "due: today";
             } else {
                 filter.value = "";
             };

             //filter.form.submit();
             unsafeWindow.control.updateListFilter();
             }, true);
         document.getElementById("tools").appendChild(button);
     }
 })();