window.onload = function() {

   var campaignQueryString = '<enter your querystring here>';  // dont forget the '?'

   // just replace '<your domain here>' with your domain, keep the '/'s and the 'i'
   var domainRegEx = /<your domain here>/i

   var links = document.getElementsByTagName('a');
   for (var i=0, len = links.length; i < len; i++) {
      var link = links[i];
      var href = link.getAttribute('href');
      if(domainRegEx.test(href)) {
         var newHref = href + campaignQueryString;
         link.setAttribute('href', newHref);
      }
   }

}