favicon from Jenkins' status

jenkins_status_favicon.user.js

// ==UserScript==
// @name           Jenkins status favicon
// @namespace      http://www.xn--n8j4d9b.com/
// @include        http://url_to_your_jenkins
// ==/UserScript==

var favicon = document.createElement('link');
favicon.rel = 'shortcut icon';
favicon.type = 'image/gif';
var img = document.getElementsByClassName('icon32x32')[0]
if(img == undefined) {
  if((img = document.getElementsByClassName('build-row')[0]) != undefined){
    img = img.getElementsByTagName('img')[0]
  }
}  
if(img != undefined) {
  favicon.href = img.src;
  document.head.appendChild(favicon);
}