Exposing first article element based on Miketay's gist https://gist.github.com/4032962

first_article.js

// ==UserScript==
// @include http://*/*
// @include https://*/*
// ==/UserScript==

//applies a "main-content" style to the first article element

var style = document.createElement('style');
style.innerHTML = ".main-content {outline: 5px dotted deeppink !important;}"
document.body.appendChild(style);

var kids = [].slice.apply(document.body.children);

for (var i = 0, l = kids.length; i < l; i++) {
  switch(kids[i].tagName.toLowerCase()){
    case "article":
      kids[i].classList.add('main-content');
      break;
    default:
      break;
  }

  break;
}