Flickering test

  window.observeCustom = {
      waitForElement: function waitForElement(selector, fn) {

          // If Mutation Observers are available
          if (window.MutationObserver || window.WebKitMutationObserver) {

              var listeners = [],
                  doc = window.document,
                  MutationObserver = window.MutationObserver || window.WebKitMutationObserver,
                  observer;

              // Store the selector and callback to be monitored
              listeners.push({
                  selector: selector,
                  fn: fn
              });

              function check() {
                  // Check the DOM for elements matching a stored selector
                  for (var i = 0, len = listeners.length, listener, elements; i < len; i++) {
                      listener = listeners[i];
                      // Query for elements matching the specified selector
                      elements = document.querySelectorAll( listener.selector );

                      for (var j = 0, jLen = elements.length, element; j < jLen; j++) {
                          element = elements[j];
                          // Make sure the callback isn't invoked with the
                          // same element more than once
                          if (!element.ready) {
                              element.ready = true;
                              // Invoke the callback with the element
                              listener.fn.call(element, element);
                          }
                      }
                  }
              }

              if (!observer) {

                  // Watch for changes in the document
                  observer = new MutationObserver(check);
                  observer.observe(doc.documentElement, {
                      childList: true,
                      subtree: true
                  });

              }

              // Check if the element is currently in the DOM
              check();

          }

      }
  };

  observeCustom.waitForElement('#logo', function(element) {
     element.src = "./v2.png";
  });