Variation of the Universal Analytics tracking Code (Google Analytics). It can only be safely included once since it overwrites itself. The original script does check against that. Also, document.scripts is not available in Firefox < 9

ga.js

(function(G,O,o,g,l,e){G.GoogleAnalyticsObject=O;G[O]=function(){G[O].q.push(arguments)},G[O].q=[],G[O].l=+new Date;e=o.createElement('script'),l=o.scripts[0];e.src=g;l.parentNode.insertBefore(e,l)}(this,'ga',document,'//www.google-analytics.com/analytics.js'));

// ===>
ga('create', 'UA-XXXXXXX-Y');
ga('send', 'pageview');

unminified-ga.js

(function(){

  // G == this == window
  // O == 'ga'
  // o == document
  // g == '//www.google-analytics.com/analytics.js'
  // l == undefined
  // e == undefined

  // the name of the Analytics object, in case 'ga' clashes with some library
  window.GoogleAnalyticsObject = 'ga';

  // the Analytics object
  window.ga = function() {

    // add a task to the Analytics queue
    window.ga.q.push(arguments);

  };

  // the Analytics queue
  window.ga.q  = [];

  // the current timestamp
  window.ga.l  = +new Date();

  // create a new script element; this is assigned to e, which is intentionally left undefined
  var script   = document.createElement('script');
  
  // scheme-agnostic script url
  script.src   = '//www.google-analytics.com/analytics.js';

  // script.async = true; is implied by every spec-conform browser (Firefox 3.6 makes an exception here)

  // insert the script element into the document; this is assigned to l, which is intentionally left undefined
  var firstScript = document.scripts[0];
  firstScript.parentNode.insertBefore(script, firstScript);

}())