to fix the code, do:

function addlilink(tabs, url, name, id){
  var na = document.createElement('a');
  na.href = url;
  na.appendChild(document.createTextNode(name));
  var li = document.createElement('li');
  if (id) li.id = id;
  li.appendChild(na);
  tabs.appendChild(li);
  return li;
}

function addTab(url, name, id){
    var tabs = document.getElementById('p-cactions').getElementsByTagName('ul')[0];
    addlilink(tabs, url, name, id);
}

function addlimenu(tabs, name, id) {
  var na = document.createElement('a');
  na.href = '';
  var mn = document.createElement('ul');
  na.appendChild(document.createTextNode(name));
  var li = document.createElement('li');
  if(id) li.id = id;
  li.className = 'tabmenu';
  li.appendChild(na);
  li.appendChild(mn);
  tabs.appendChild(li);
  return li;
}

// ===== My Script =====
funciton doQwikify() {
  alert('test');
}
function addQwikify() {
  addTab("javascript:doQwikify()", "dqw", "")
}

if (window.addEventListener) window.addEventListener("load", addQwikify, false);
else if (window.attachEvent) window.attachEvent("onload", addQwikify);

// ========== Edit Section 0 ==========
function addEditSection0() {
  ta['ca-edit-0'] = ['', 'Edit the zeroth section of this page'];
  if (!document.getElementById) return;
  x = document.getElementById('ca-edit');
  if(!x) return;
  y = document.createElement('LI');
  y.id = 'ca-edit-0';
  if (x.className == 'selected') {
    if (/&action=edit&section=0$/.test(window.location.href)) {
      x.className = 'istalk';
      y.className = 'selected';
    } else {
      x.className = 'selected istalk';
    }
  } else if (x.className == 'selected istalk') {
    if (/&action=edit&section=0$/.test(window.location.href)) {
      x.className = 'istalk';
      y.className = 'selected istalk';
    } else {
      y.className = 'istalk';
    }
  } else {
    y.className = x.className;
    x.className = 'istalk';
  }
  z = document.createElement('A');
  if (x.children) {
    z.href = x.children[0].href + '&section=0';
    z.appendChild(document.createTextNode('0'));
    y.appendChild(z);
    document.getElementById('p-cactions').children[1].insertBefore(y,x.nextSibling);
  } else {
    z.href = x.childNodes[0].href + '&section=0';
    z.appendChild(document.createTextNode('0'));
    y.appendChild(z);
    document.getElementById('p-cactions').childNodes[3].insertBefore(y,x.nextSibling);
  }
}

if (window.addEventListener) window.addEventListener("load", addEditSection0, false);
else if (window.attachEvent) window.attachEvent("onload", addEditSection0);

// ========== Add Last Diff ==========

function doLastDiff() {
 z=document.getElementById("content").childNodes;
 for (var n=0;n<z.length;n++) { 
   if (z[n].className=="firstHeading") {
     var pname=z[n].textContent;
   };
 };
 var nurl="http://en.wikipedia.org/w/index.php?title=" + pname + "&diff=cur&oldid=prev";
 document.location=nurl
}
function addLastDiff() {
    var tabs = document.getElementById('p-cactions').getElementsByTagName('ul')[0];
    var l=addlilink(tabs, "javascript:doLastDiff()", 'last', '');
    l.lastChild.title="Show most recent diff";
}

if (window.addEventListener) window.addEventListener("load", addLastDiff, false);
else if (window.attachEvent) window.attachEvent("onload", addLastDiff);