only in patch2:
unchanged:
--- a/core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php
@@ -88,11 +88,15 @@ public function waitForElement($selector, $locator, $timeout = 10000) {
    * @see \Behat\Mink\Element\ElementInterface::findAll()
    */
   public function waitForElementVisible($selector, $locator, $timeout = 10000) {
-    $page = $this->session->getPage();
+    $session = $this->session;
+    $page = $session->getPage();
 
-    $result = $page->waitFor($timeout / 1000, function() use ($page, $selector, $locator) {
+    $result = $page->waitFor($timeout / 1000, function() use ($session, $page, $selector, $locator, $timeout) {
       $element = $page->find($selector, $locator);
       if (!empty($element) && $element->isVisible()) {
+        // Make sure no elements are animating before returning.
+        $session->wait($timeout, "(typeof jQuery === 'undefined' || jQuery(':animated').length === 0)");
+
         return $element;
       }
       return NULL;