diff --git i/src/wp-includes/class-wp-customize-nav-menus.php w/src/wp-includes/class-wp-customize-nav-menus.php
index e263e3f391..d1985b9ad8 100644
--- i/src/wp-includes/class-wp-customize-nav-menus.php
+++ w/src/wp-includes/class-wp-customize-nav-menus.php
@@ -1132,7 +1132,7 @@ final class WP_Customize_Nav_Menus {
 		add_action( 'wp_enqueue_scripts', array( $this, 'customize_preview_enqueue_deps' ) );
 		add_filter( 'wp_nav_menu_args', array( $this, 'filter_wp_nav_menu_args' ), 1000 );
 		add_filter( 'wp_nav_menu', array( $this, 'filter_wp_nav_menu' ), 10, 2 );
-		add_filter( 'wp_footer', array( $this, 'export_preview_data' ), 1 );
+		add_action( 'wp_footer', array( $this, 'export_preview_data' ), 1 );
 		add_filter( 'customize_render_partials_response', array( $this, 'export_partial_rendered_nav_menu_instances' ) );
 	}
 
diff --git i/src/wp-includes/js/tinymce/plugins/wordpress/plugin.js w/src/wp-includes/js/tinymce/plugins/wordpress/plugin.js
index 08e3cf78c9..b32cf2c893 100644
--- i/src/wp-includes/js/tinymce/plugins/wordpress/plugin.js
+++ w/src/wp-includes/js/tinymce/plugins/wordpress/plugin.js
@@ -1,7 +1,9 @@
 /* global getUserSetting, setUserSetting */
 ( function( tinymce ) {
-// Set the minimum value for the modals z-index higher than #wpadminbar (100000)
-tinymce.ui.FloatPanel.zIndex = 100100;
+// Set the minimum value for the modals z-index higher than .wp-full-overlay (500000)
+if ( tinymce.ui.FloatPanel.zIndex < 500001 ) {
+	tinymce.ui.FloatPanel.zIndex = 500001;
+}
 
 tinymce.PluginManager.add( 'wordpress', function( editor ) {
 	var wpAdvButton, style,