diff -u b/core/misc/collapse.js b/core/misc/collapse.js
--- b/core/misc/collapse.js
+++ b/core/misc/collapse.js
@@ -106,38 +106,29 @@
     },
 
     /**
-     * Toggle the visibility of a details element using smooth animations.
+     * Toggle the visibility of a details element.
      */
-    toggle: function (isOpen) {
-      if (typeof isOpen == 'undefined') {
-        isOpen = !this.$node.attr('open');
-      }
-
-      if (!Modernizr.details) {
-        var $summaryPrefix = this.$node.find('> summary span.details-summary-prefix');
-        if (isOpen) {
-          $summaryPrefix.html(Drupal.t('Hide'));
-        }
-        else {
-          $summaryPrefix.html(Drupal.t('Show'));
-        }
-        // Delay setting the attribute to emulate chrome behavior and make
-        // details-aria.js work as expected with this polyfill.
-        setTimeout(function () {
-          this.$node.attr('open', isOpen);
-        }.bind(this), 0);
+    toggle: function () {
+      var isOpen = !!this.$node.attr('open');
+      var $summaryPrefix = this.$node.find('> summary span.details-summary-prefix');
+      if (isOpen) {
+        $summaryPrefix.html(Drupal.t('Show'));
       }
       else {
-        this.$node.attr('open', isOpen);
+        $summaryPrefix.html(Drupal.t('Hide'));
       }
-
+      // Delay setting the attribute to emulate chrome behavior and make
+      // details-aria.js work as expected with this polyfill.
+      setTimeout(function () {
+        this.$node.attr('open', !isOpen);
+      }.bind(this), 0);
     },
 
     /**
      * Handle invalid event
      */
     invalidHandler: function () {
-      this.toggle(true);
+      this.$node.find('> summary').trigger('click');
     }
   });