diff -u b/core/modules/ckeditor/ckeditor.module b/core/modules/ckeditor/ckeditor.module
--- b/core/modules/ckeditor/ckeditor.module
+++ b/core/modules/ckeditor/ckeditor.module
@@ -92,6 +92,19 @@
 }
 
 /**
+ * Implements hook_page_build().
+ */
+function ckeditor_page_build(&$page) {
+  // Add our CSS file that adds common needed classes, such as align-left,
+  // align-right, underline, indent, etc.
+  // @todo The CSS in this file needs to continue to be applied even after
+  //   disabling ckeditor.module after CKEditor-edited content is saved,
+  //   so move it to somewhere global, such as system.base.css:
+  //   http://drupal.org/node/1904976.
+  $page['#attached']['library'][] = array('ckeditor', 'drupal.ckeditor.css');
+}
+
+/**
  * Retrieves the default theme's CKEditor stylesheets defined in the .info file.
  *
  * Themes may specify iframe-specific CSS files for use with CKEditor by
diff -u b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/ckeditor/plugin/Internal.php b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/ckeditor/plugin/Internal.php
--- b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/ckeditor/plugin/Internal.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/ckeditor/plugin/Internal.php
@@ -45,6 +45,7 @@
   public function getConfig(Editor $editor) {
     // Reasonable defaults that provide expected basic behavior.
     $config = array(
+      'customConfig' => '', // Don't load CKEditor's config.js file.
       'pasteFromWordPromptCleanup' => TRUE,
       'indentClasses' => array('indent1', 'indent2', 'indent3'),
       'justifyClasses' => array('align-left', 'align-center', 'align-right', 'align-justify'),
diff -u b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorAdminTest.php b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorAdminTest.php
--- b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorAdminTest.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorAdminTest.php
@@ -68,31 +68,52 @@
     $this->assertTrue(((string) $options[1]) === 'CKEditor', 'Option 2 in the Text Editor select is "CKEditor".');
     $this->assertTrue(((string) $options[0]['selected']) === 'selected', 'Option 1 ("None") is selected.');
 
+    // Ensure the CKEditor editor returns the expected default settings.
+    $expected_default_settings = array(
+      'toolbar' => array(
+        'buttons' => array(
+          array(
+            'Bold', 'Italic',
+            '|', 'Link', 'Unlink',
+            '|', 'BulletedList', 'NumberedList',
+            '|', 'Blockquote', 'Image',
+            '|', 'Source',
+          ),
+        ),
+      ),
+      'plugins' => array(),
+    );
+    $this->assertIdentical($ckeditor->getDefaultSettings(), $expected_default_settings);
+
     // Select the "CKEditor" editor and click the "Configure" button.
     $edit = array(
       'editor[editor]' => 'ckeditor',
     );
-    // $this->drupalPost(NULL, $edit, t('Configure'));
     $this->drupalPostAjax(NULL, $edit, 'editor_configure');
     $editor = entity_load('editor', 'filtered_html');
     $this->assertFalse($editor, 'No Editor config entity exists yet.');
 
-    // Default configuration.
-    $default_buttons_value = '[["Source","|","Bold","Italic","|","NumberedList","BulletedList","Blockquote","|","JustifyLeft","JustifyCenter","JustifyRight","|","Link","Unlink","|","Image","Maximize"]]';
-    $this->assertFieldByName('editor[settings][toolbar][buttons]', $default_buttons_value, 'Buttons configuration');
+    // Ensure the toolbar buttons configuration value is initialized to the
+    // expected default value.
+    $expected_buttons_value = json_encode($expected_default_settings['toolbar']['buttons']);
+    $this->assertFieldByName('editor[settings][toolbar][buttons]', $expected_buttons_value);
+
+    // Ensure the styles textarea exists and is initialized empty.
     $styles_textarea = $this->xpath('//textarea[@name="editor[settings][plugins][stylescombo][styles]"]');
     $this->assertFieldByXPath('//textarea[@name="editor[settings][plugins][stylescombo][styles]"]', '', 'The styles textarea exists and is empty.');
     $this->assertTrue(count($styles_textarea) === 1, 'The "styles" textarea exists.');
+
+    // Submit the form to save the selection of CKEditor as the chosen editor.
     $this->drupalPost(NULL, $edit, t('Save configuration'));
 
     // Ensure an Editor object exists now, with the proper settings.
-    $expected_settings = $ckeditor->getDefaultSettings();
+    $expected_settings = $expected_default_settings;
     $expected_settings['plugins']['stylescombo']['styles'] = '';
     $editor = entity_load('editor', 'filtered_html');
     $this->assertTrue($editor instanceof Editor, 'An Editor config entity exists now.');
     $this->assertIdentical($expected_settings, $editor->settings, 'The Editor config entity has the correct settings.');
 
-    // Configure a plugin.
+    // Configure the Styles plugin, and ensure the updated settings are saved.
     $edit = array(
       'editor[settings][plugins][stylescombo][styles]' => "Title|h1.title\nCallout|p.callout\n\n",
     );
@@ -102,15 +123,17 @@
     $this->assertTrue($editor instanceof Editor, 'An Editor config entity exists.');
     $this->assertIdentical($expected_settings, $editor->settings, 'The Editor config entity has the correct settings.');
 
-    // "Drag and drop" buttons: remove one button, add a separator, add a button
-    // and finally, add a button to a new row.
+    // Change the buttons that appear on the toolbar (in JavaScript, this is
+    // done via drag and drop, but here we can only emulate the end result of
+    // that interaction). Test multiple toolbar rows and a divider within a row.
+    $expected_settings['toolbar']['buttons'] = array(
+      array('Undo', '|', 'Redo'),
+      array('JustifyCenter'),
+    );
     $edit = array(
-      'editor[settings][toolbar][buttons]' => '[["Source","|","Bold","Italic","|","NumberedList","BulletedList","Blockquote","|","JustifyLeft","JustifyCenter","JustifyRight","|","Link","Unlink","|","Image","|","Undo"],["Redo"]]'
+      'editor[settings][toolbar][buttons]' => json_encode($expected_settings['toolbar']['buttons']),
     );
     $this->drupalPost(NULL, $edit, t('Save configuration'));
-    $expected_settings['toolbar']['buttons'][0][17] = '|';
-    $expected_settings['toolbar']['buttons'][0][18] = 'Undo';
-    $expected_settings['toolbar']['buttons'][1][] = 'Redo';
     $editor = entity_load('editor', 'filtered_html');
     $this->assertTrue($editor instanceof Editor, 'An Editor config entity exists.');
     $this->assertIdentical($expected_settings, $editor->settings, 'The Editor config entity has the correct settings.');
diff -u b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorTest.php b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorTest.php
--- b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorTest.php
@@ -92,9 +92,9 @@
     $editor->settings['toolbar']['buttons'][1][] = 'Format';
     $editor->settings['plugins']['internal']['link_shortcut'] = 'CTRL+K';
     $editor->save();
-    $expected_config['toolbar'][5]['items'][] = 'Underline';
-    $expected_config['toolbar'][7]['items'][] = 'Format';
-    $expected_config['toolbar'][8] = '/';
+    $expected_config['toolbar'][count($expected_config['toolbar'])-2]['items'][] = 'Underline';
+    $expected_config['toolbar'][]['items'][] = 'Format';
+    $expected_config['toolbar'][] = '/';
     $expected_config['format_tags'] = 'p;h4;h5;h6';
     $expected_config['extraPlugins'] = 'llama_contextual,llama_contextual_and_button';
     $expected_config['drupalExternalPlugins']['llama_contextual'] = file_create_url('core/modules/ckeditor/tests/modules/js/llama_contextual.js');
@@ -125,7 +125,7 @@
     // Customize the configuration.
     $editor->settings['toolbar']['buttons'][0][] = 'Underline';
     $editor->save();
-    $expected[5]['items'][] = 'Underline';
+    $expected[count($expected)-2]['items'][] = 'Underline';
     $this->assertIdentical($expected, $this->ckeditor->buildToolbarJSSetting($editor), '"toolbar" configuration part of JS settings built correctly for customized toolbar.');
 
     // Enable the editor_test module, customize further.
@@ -133,7 +133,7 @@
     drupal_container()->get('plugin.manager.ckeditor.plugin')->clearCachedDefinitions();
     $editor->settings['toolbar']['buttons'][0][] = 'Llama';
     $editor->save();
-    $expected[5]['items'][] = 'Llama';
+    $expected[count($expected)-2]['items'][] = 'Llama';
     $this->assertIdentical($expected, $this->ckeditor->buildToolbarJSSetting($editor), '"toolbar" configuration part of JS settings built correctly for customized toolbar with contrib module-provided CKEditor plugin.');
   }
 
@@ -225,6 +225,7 @@
 
   protected function getDefaultInternalConfig() {
     return array(
+      'customConfig' => '',
       'pasteFromWordPromptCleanup' => TRUE,
       'indentClasses' => array('indent1', 'indent2', 'indent3'),
       'justifyClasses' => array('align-left', 'align-center', 'align-right', 'align-justify'),
@@ -241,13 +242,12 @@
 
   protected function getDefaultToolbarConfig() {
     return array(
-      0 => array('items' => array('Source')),
-      1 => array('items' => array('Bold', 'Italic')),
-      2 => array('items' => array('NumberedList', 'BulletedList', 'Blockquote')),
-      3 => array('items' => array('JustifyLeft', 'JustifyCenter', 'JustifyRight')),
-      4 => array('items' => array('Link', 'Unlink')),
-      5 => array('items' => array('Image', 'Maximize')),
-      6 => '/'
+      0 => array('items' => array('Bold', 'Italic')),
+      1 => array('items' => array('Link', 'Unlink')),
+      2 => array('items' => array('BulletedList', 'NumberedList')),
+      3 => array('items' => array('Blockquote', 'Image')),
+      4 => array('items' => array('Source')),
+      5 => '/'
     );
   }