// ==UserScript==
// @include http://somesite
// ==/UserScript==

document.addEventListener('DOMContentLoaded',function() {
  var identifier = "I'm Feeling Lucky"

  var attrs = ['action','defaultValue','value','name','src','','="'+identifier+'" or @'];
  attrs = ('@'+attrs.join(attrs.pop())).slice(0,-5);
  var lnk = document.selectSingleNode('//a[@href="'+identifier+'" or text()="'+identifier+'"]|//button['+attrs+' or text()="'+identifier+'"]|//input[(@type="submit" or @type="image" or @type="button") and ('+attrs+')]');
  if( lnk ) { lnk.click(); }
},false);