reverted:
--- b/core/tests/Drupal/Tests/BrowserTestBase.php
+++ a/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -1407,7 +1407,7 @@
    *   Either the new page content or FALSE.
    */
   protected function checkForMetaRefresh() {
+    $refresh = $this->cssSelect('meta[http-equiv="Refresh"]');
-    $refresh = $this->cssSelect('meta[http-equiv="Refresh"], meta[http-equiv="refresh"]');
     if (!empty($refresh) && (!isset($this->maximumMetaRefreshCount) || $this->metaRefreshCount < $this->maximumMetaRefreshCount)) {
       // Parse the content attribute of the meta tag for the format:
       // "[delay]: URL=[page_to_redirect_to]".