diff -u b/core/misc/form.js b/core/misc/form.js
--- b/core/misc/form.js
+++ b/core/misc/form.js
@@ -196,13 +196,14 @@
   Drupal.behaviors.fillUserInfoFromBrowser = {
     attach: function (context, settings) {
       var userInfo = ['name', 'mail', 'homepage'];
-      var $forms = $('form.user-info-from-browser').once('user-info-from-browser');
+      var $forms = $('[user-info-from-browser]').once('user-info-from-browser');
       if ($forms.length) {
         var browserData;
         userInfo.map(function (info) {
           var $element = $forms.find('[name=' + info + ']');
           browserData = localStorage.getItem('Drupal.visitor.' + info);
-          if ($element.length && ($element.val() === '' || ($element.attr('data-drupal-default-value') === $element.val())) && browserData) {
+          var emptyOrDefault = ($element.val() === '' || ($element.attr('data-drupal-default-value') === $element.val()));
+          if ($element.length && emptyOrDefault && browserData) {
             $element.val(browserData);
           }
         });
diff -u b/core/modules/comment/lib/Drupal/comment/CommentFormController.php b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
--- b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
@@ -100,7 +100,7 @@
 
     if (!$this->currentUser->isAuthenticated() && $anonymous_contact != COMMENT_ANONYMOUS_MAYNOT_CONTACT) {
       $form['#attached']['library'][] = 'core/drupal.form';
-      $form['#attributes']['class'][] = 'user-info-from-browser';
+      $form['#attributes']['user-info-from-browser'] = TRUE;
     }
 
     // If not replying to a comment, use our dedicated page callback for new
diff -u b/core/modules/contact/lib/Drupal/contact/MessageFormController.php b/core/modules/contact/lib/Drupal/contact/MessageFormController.php
--- b/core/modules/contact/lib/Drupal/contact/MessageFormController.php
+++ b/core/modules/contact/lib/Drupal/contact/MessageFormController.php
@@ -54,7 +54,7 @@
     );
     if ($user->isAnonymous()) {
       $form['#attached']['library'][] = 'core/drupal.form';
-      $form['#attributes']['class'][] = 'user-info-from-browser';
+      $form['#attributes']['user-info-from-browser'] = TRUE;
     }
     // Do not allow authenticated users to alter the name or e-mail values to
     // prevent the impersonation of other users.
diff -u b/core/modules/user/lib/Drupal/user/RegisterFormController.php b/core/modules/user/lib/Drupal/user/RegisterFormController.php
--- b/core/modules/user/lib/Drupal/user/RegisterFormController.php
+++ b/core/modules/user/lib/Drupal/user/RegisterFormController.php
@@ -44,7 +44,7 @@
       return new RedirectResponse(url('user/' . \Drupal::currentUser()->id(), array('absolute' => TRUE)));
     }
 
-    $form['#attributes']['class'][] = 'user-info-from-browser';
+    $form['#attributes']['user-info-from-browser'] = TRUE;
 
     // Start with the default user account fields.
     $form = parent::form($form, $form_state, $account);