diff --git a/src/wp-includes/class-wp-editor.php b/src/wp-includes/class-wp-editor.php
index 1846214e3c..47d82ecacb 100644
--- a/src/wp-includes/class-wp-editor.php
+++ b/src/wp-includes/class-wp-editor.php
@@ -317,9 +317,11 @@ final class _WP_Editors {
 		if ( empty( self::$first_init ) ) {
 			if ( is_admin() ) {
 				add_action( 'admin_print_footer_scripts', array( __CLASS__, 'editor_js' ), 50 );
+				add_action( 'admin_print_footer_scripts', array( __CLASS__, 'force_uncompressed_tinymce' ), 1 );
 				add_action( 'admin_print_footer_scripts', array( __CLASS__, 'enqueue_scripts' ), 1 );
 			} else {
 				add_action( 'wp_print_footer_scripts', array( __CLASS__, 'editor_js' ), 50 );
+				add_action( 'wp_print_footer_scripts', array( __CLASS__, 'force_uncompressed_tinymce' ), 1 );
 				add_action( 'wp_print_footer_scripts', array( __CLASS__, 'enqueue_scripts' ), 1 );
 			}
 		}
@@ -755,6 +757,9 @@ final class _WP_Editors {
 	}
 
 	/**
+	 *
+	 * @static
+	 *
 	 * @param bool $default_scripts Optional. Whether default scripts should be enqueued. Default false.
 	 */
 	public static function enqueue_scripts( $default_scripts = false ) {
@@ -819,8 +824,10 @@ final class _WP_Editors {
 		wp_enqueue_style( 'editor-buttons' );
 
 		if ( is_admin() ) {
+			add_action( 'admin_print_footer_scripts', array( __CLASS__, 'force_uncompressed_tinymce' ), 1 );
 			add_action( 'admin_print_footer_scripts', array( __CLASS__, 'print_default_editor_scripts' ), 45 );
 		} else {
+			add_action( 'wp_print_footer_scripts', array( __CLASS__, 'force_uncompressed_tinymce' ), 1 );
 			add_action( 'wp_print_footer_scripts', array( __CLASS__, 'print_default_editor_scripts' ), 45 );
 		}
 	}
@@ -1387,6 +1394,32 @@ final class _WP_Editors {
 			"tinymce.ScriptLoader.markDone( '$baseurl/langs/$mce_locale.js' );\n";
 	}
 
+	/**
+	 * Force uncompressed TinyMCE when a custom theme has been defined.
+	 *
+	 * The compressed TinyMCE file cannot deal with custom themes, so this makes
+	 * sure that we use the uncompressed TinyMCE file if a theme is defined.
+	 * Even if we are on a production environment.
+	 */
+	public static function force_uncompressed_tinymce() {
+		$has_custom_theme = false;
+		foreach ( self::$mce_settings as $init ) {
+			if ( ! empty( $init['theme_url'] ) ) {
+				$has_custom_theme = true;
+				break;
+			}
+		}
+
+		if ( ! $has_custom_theme ) {
+			return;
+		}
+
+		$wp_scripts = wp_scripts();
+
+		$wp_scripts->remove( 'wp-tinymce' );
+		wp_register_tinymce_scripts( $wp_scripts, true );
+	}
+
 	/**
 	 * Print (output) the main TinyMCE scripts.
 	 *
@@ -1397,7 +1430,7 @@ final class _WP_Editors {
 	 * @global bool   $compress_scripts
 	 */
 	public static function print_tinymce_scripts() {
-		global $tinymce_version, $concatenate_scripts, $compress_scripts;
+		global $concatenate_scripts;
 
 		if ( self::$tinymce_scripts_printed ) {
 			return;
@@ -1408,33 +1441,6 @@ final class _WP_Editors {
 		if ( ! isset( $concatenate_scripts ) ) {
 			script_concat_settings();
 		}
-
-		$suffix  = SCRIPT_DEBUG ? '' : '.min';
-		$version = 'ver=' . $tinymce_version;
-		$baseurl = self::get_baseurl();
-
-		$has_custom_theme = false;
-		foreach ( self::$mce_settings as $init ) {
-			if ( ! empty( $init['theme_url'] ) ) {
-				$has_custom_theme = true;
-				break;
-			}
-		}
-
-		$compressed = $compress_scripts && $concatenate_scripts && isset( $_SERVER['HTTP_ACCEPT_ENCODING'] )
-			&& false !== stripos( $_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip' ) && ! $has_custom_theme;
-
-		// Load tinymce.js when running from /src, else load wp-tinymce.js.gz (production) or tinymce.min.js (SCRIPT_DEBUG)
-		$mce_suffix = false !== strpos( get_bloginfo( 'version' ), '-src' ) ? '' : '.min';
-
-		if ( $compressed ) {
-			echo "<script type='text/javascript' src='{$baseurl}/wp-tinymce.php?c=1&amp;$version'></script>\n";
-		} else {
-			echo "<script type='text/javascript' src='{$baseurl}/tinymce{$mce_suffix}.js?$version'></script>\n";
-			echo "<script type='text/javascript' src='{$baseurl}/plugins/compat3x/plugin{$suffix}.js?$version'></script>\n";
-		}
-
-		echo "<script type='text/javascript'>\n" . self::wp_mce_translation() . "</script>\n";
 	}
 
 	/**
diff --git a/src/wp-includes/default-filters.php b/src/wp-includes/default-filters.php
index 9989957b14..c36ba799cf 100644
--- a/src/wp-includes/default-filters.php
+++ b/src/wp-includes/default-filters.php
@@ -502,6 +502,8 @@ add_action( 'set_current_user', 'kses_init' );
 
 // Script Loader
 add_action( 'wp_default_scripts', 'wp_default_scripts' );
+add_action( 'wp_default_scripts', 'wp_default_packages' );
+
 add_action( 'wp_enqueue_scripts', 'wp_localize_jquery_ui_datepicker', 1000 );
 add_action( 'admin_enqueue_scripts', 'wp_localize_jquery_ui_datepicker', 1000 );
 add_action( 'admin_print_scripts-index.php', 'wp_localize_community_events' );
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 262020ac7b..a5b502c942 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -41,22 +41,26 @@ require( ABSPATH . WPINC . '/functions.wp-styles.php' );
  *
  * @param WP_Scripts $scripts WP_Scripts object.
  */
-function wp_register_tinymce_scripts( &$scripts ) {
+function wp_register_tinymce_scripts( &$scripts, $force_uncompressed = false ) {
 	global $tinymce_version, $concatenate_scripts, $compress_scripts;
-	$suffix     = SCRIPT_DEBUG ? '' : '.min';
+	$suffix = SCRIPT_DEBUG ? '' : '.min';
+
+	script_concat_settings();
+
 	$compressed = $compress_scripts && $concatenate_scripts && isset( $_SERVER['HTTP_ACCEPT_ENCODING'] )
-				  && false !== stripos( $_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip' );
+				  && false !== stripos( $_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip' ) && ! $force_uncompressed;
+
 	// Load tinymce.js when running from /src, otherwise load wp-tinymce.js.gz (in production) or
 	// tinymce.min.js (when SCRIPT_DEBUG is true).
 	$mce_suffix = false !== strpos( get_bloginfo( 'version' ), '-src' ) ? '' : '.min';
 	if ( $compressed ) {
 		$scripts->add( 'wp-tinymce', includes_url( 'js/tinymce/' ) . 'wp-tinymce.php', array(), $tinymce_version );
 	} else {
-		$scripts->add( 'wp-tinymce-root', includes_url( 'js/tinymce/' ) . "tinymce{$mce_suffix}.js", array(), $tinymce_version );
-		$scripts->add( 'wp-tinymce', includes_url( 'js/tinymce/' ) . "plugins/compat3x/plugin{$suffix}.js", array( 'wp-tinymce-root' ), $tinymce_version );
+		$scripts->add( 'wp-tinymce-root', includes_url( 'js/tinymce/' ) . "tinymce$mce_suffix.js", array(), $tinymce_version );
+		$scripts->add( 'wp-tinymce', includes_url( 'js/tinymce/' ) . "plugins/compat3x/plugin$suffix.js", array( 'wp-tinymce-root' ), $tinymce_version );
 	}
 
-	$scripts->add( 'wp-tinymce-lists', includes_url( 'js/tinymce/plugins/lists/index' . $suffix . '.js', array( 'wp-tinymce' ), $tinymce_version ) );
+	$scripts->add( 'wp-tinymce-lists', includes_url( "js/tinymce/plugins/lists/plugin$suffix.js", array( 'wp-tinymce' ), $tinymce_version ) );
 }
 
 /**
@@ -69,9 +73,11 @@ function wp_register_tinymce_scripts( &$scripts ) {
  *
  * @param WP_Scripts $scripts WP_Scripts object.
  */
-function wp_default_packages_vendor( &$scripts, $dev_suffix ) {
+function wp_default_packages_vendor( &$scripts ) {
 	wp_register_tinymce_scripts( $scripts );
 
+	$dev_suffix = wp_scripts_get_suffix( 'dev' );
+
 	$vendor_scripts = array(
 		'react',
 		'react-dom' => array( 'react' ),
@@ -90,7 +96,7 @@ function wp_default_packages_vendor( &$scripts, $dev_suffix ) {
 			$dependencies = array();
 		}
 
-		$path = '/js/dist/vendor/' . $handle . $dev_suffix . '.js';
+		$path = "/js/dist/vendor/$handle$dev_suffix.js";
 
 		$scripts->add( $handle, $path, $dependencies, false, 1 );
 	}
@@ -124,7 +130,7 @@ function wp_default_packages_vendor( &$scripts, $dev_suffix ) {
  * @param array      $tests   Features to detect.
  * @return string Conditional polyfill inline script.
  */
-function wp_get_script_polyfill( $scripts, $tests ) {
+function wp_get_script_polyfill( &$scripts, $tests ) {
 	$polyfill = '';
 	foreach ( $tests as $test => $handle ) {
 		if ( ! array_key_exists( $handle, $scripts->registered ) ) {
@@ -147,7 +153,7 @@ function wp_get_script_polyfill( $scripts, $tests ) {
 }
 
 /**
- * Register all the WordPress packages scripts that are in the standardized
+ * Registers all the WordPress packages scripts that are in the standardized
  * `js/dist/` location.
  *
  * For the order of `$scripts->add` see `wp_default_scripts`.
@@ -155,9 +161,10 @@ function wp_get_script_polyfill( $scripts, $tests ) {
  * @since 5.0.0
  *
  * @param WP_Scripts $scripts WP_Scripts object.
- * @param string     $suffix  The suffix to use before `.js`.
  */
-function wp_default_packages_scripts( &$scripts, $suffix ) {
+function wp_default_packages_scripts( &$scripts ) {
+	$suffix = wp_scripts_get_suffix();
+
 	$packages_dependencies = array(
 		'api-fetch'                          => array( 'wp-polyfill', 'wp-hooks', 'wp-i18n' ),
 		'a11y'                               => array( 'wp-dom-ready', 'wp-polyfill' ),
@@ -330,7 +337,7 @@ function wp_default_packages_scripts( &$scripts, $suffix ) {
 
 	foreach ( $packages_dependencies as $package => $dependencies ) {
 		$handle = 'wp-' . $package;
-		$path   = '/js/dist/' . $package . $suffix . '.js';
+		$path   = "/js/dist/$package$suffix.js";
 
 		$scripts->add( $handle, $path, $dependencies, false, 1 );
 	}
@@ -422,12 +429,14 @@ function wp_default_packages_inline_scripts( &$scripts ) {
 		'after'
 	);
 
+	/* This filter is documented in wp-includes/class-wp-editor.php */
 	$tinymce_settings = apply_filters(
 		'tiny_mce_before_init',
 		array(
 			'plugins'          => implode(
 				',',
 				array_unique(
+					/* This filter is documented in wp-includes/class-wp-editor.php */
 					apply_filters(
 						'tiny_mce_plugins',
 						array(
@@ -456,6 +465,7 @@ function wp_default_packages_inline_scripts( &$scripts ) {
 			'toolbar1'         => implode(
 				',',
 				array_merge(
+					/* This filter is documented in wp-includes/class-wp-editor.php */
 					apply_filters(
 						'mce_buttons',
 						array(
@@ -481,6 +491,7 @@ function wp_default_packages_inline_scripts( &$scripts ) {
 			),
 			'toolbar2'         => implode(
 				',',
+				/* This filter is documented in wp-includes/class-wp-editor.php */
 				apply_filters(
 					'mce_buttons_2',
 					array(
@@ -499,8 +510,11 @@ function wp_default_packages_inline_scripts( &$scripts ) {
 					'editor'
 				)
 			),
+			/* This filter is documented in wp-includes/class-wp-editor.php */
 			'toolbar3'         => implode( ',', apply_filters( 'mce_buttons_3', array(), 'editor' ) ),
+			/* This filter is documented in wp-includes/class-wp-editor.php */
 			'toolbar4'         => implode( ',', apply_filters( 'mce_buttons_4', array(), 'editor' ) ),
+			/* This filter is documented in wp-includes/class-wp-editor.php */
 			'external_plugins' => apply_filters( 'mce_external_plugins', array() ),
 		),
 		'editor'
@@ -524,6 +538,60 @@ function wp_default_packages_inline_scripts( &$scripts ) {
 	);
 }
 
+/**
+ * Registers all the WordPress packages scripts.
+ *
+ * @since 5.0.0
+ *
+ * @param WP_Scripts $scripts WP_Scripts object.
+ */
+function wp_default_packages( &$scripts ) {
+	wp_default_packages_vendor( $scripts );
+	wp_register_tinymce_scripts( $scripts );
+	wp_default_packages_scripts( $scripts );
+
+	if ( did_action( 'init' ) ) {
+		wp_default_packages_inline_scripts( $scripts );
+	}
+}
+
+/**
+ * Returns the suffix that can be used for the scripts.
+ *
+ * There are two suffix types, the normal one and the dev suffix.
+ *
+ * @since 5.0.0
+ *
+ * @param string $type The type of suffix to retrieve.
+ * @return string The script suffix.
+ */
+function wp_scripts_get_suffix( $type = '' ) {
+	static $suffixes;
+
+	if ( $suffixes === null ) {
+		include( ABSPATH . WPINC . '/version.php' ); // include an unmodified $wp_version
+
+		$develop_src = false !== strpos( $wp_version, '-src' );
+
+		if ( ! defined( 'SCRIPT_DEBUG' ) ) {
+			define( 'SCRIPT_DEBUG', $develop_src );
+		}
+		$suffix     = SCRIPT_DEBUG ? '' : '.min';
+		$dev_suffix = $develop_src ? '' : '.min';
+
+		$suffixes = array(
+			'suffix'     => $suffix,
+			'dev_suffix' => $dev_suffix,
+		);
+	}
+
+	if ( $type === 'dev' ) {
+		return $suffixes['dev_suffix'];
+	}
+
+	return $suffixes['suffix'];
+}
+
 /**
  * Register all WordPress scripts.
  *
@@ -536,13 +604,8 @@ function wp_default_packages_inline_scripts( &$scripts ) {
  * @param WP_Scripts $scripts WP_Scripts object.
  */
 function wp_default_scripts( &$scripts ) {
-	include( ABSPATH . WPINC . '/version.php' ); // include an unmodified $wp_version
-
-	$develop_src = false !== strpos( $wp_version, '-src' );
-
-	if ( ! defined( 'SCRIPT_DEBUG' ) ) {
-		define( 'SCRIPT_DEBUG', $develop_src );
-	}
+	$suffix     = wp_scripts_get_suffix();
+	$dev_suffix = wp_scripts_get_suffix( 'dev' );
 
 	if ( ! $guessurl = site_url() ) {
 		$guessed_url = true;
@@ -554,9 +617,6 @@ function wp_default_scripts( &$scripts ) {
 	$scripts->default_version = get_bloginfo( 'version' );
 	$scripts->default_dirs    = array( '/wp-admin/js/', '/wp-includes/js/' );
 
-	$suffix     = SCRIPT_DEBUG ? '' : '.min';
-	$dev_suffix = $develop_src ? '' : '.min';
-
 	$scripts->add( 'utils', "/wp-includes/js/utils$suffix.js" );
 	did_action( 'init' ) && $scripts->localize(
 		'utils',
@@ -624,7 +684,7 @@ function wp_default_scripts( &$scripts ) {
 
 	$scripts->add( 'colorpicker', "/wp-includes/js/colorpicker$suffix.js", array( 'prototype' ), '3517m' );
 
-	$scripts->add( 'editor', "/wp-admin/js/editor$suffix.js", array( 'utils', 'jquery' ), false, 1 );
+	$scripts->add( 'editor', "/wp-admin/js/editor$suffix.js", array( 'wp-tinymce', 'utils', 'jquery' ), false, 1 );
 
 	// Back-compat for old DFW. To-do: remove at the end of 2016.
 	$scripts->add( 'wp-fullscreen-stub', "/wp-admin/js/wp-fullscreen-stub$suffix.js", array(), false, 1 );
@@ -1210,12 +1270,6 @@ function wp_default_scripts( &$scripts ) {
 
 	$scripts->add( 'wp-api', "/wp-includes/js/wp-api$suffix.js", array( 'jquery', 'backbone', 'underscore', 'wp-api-request' ), false, 1 );
 
-	wp_default_packages_vendor( $scripts, $dev_suffix );
-	wp_default_packages_scripts( $scripts, $suffix );
-	if ( did_action( 'init' ) ) {
-		wp_default_packages_inline_scripts( $scripts );
-	}
-
 	if ( is_admin() ) {
 		$scripts->add( 'admin-tags', "/wp-admin/js/tags$suffix.js", array( 'jquery', 'wp-ajax-response' ), false, 1 );
 		did_action( 'init' ) && $scripts->localize(
diff --git a/tests/phpunit/tests/dependencies/scripts.php b/tests/phpunit/tests/dependencies/scripts.php
index dba0908248..8e30f93fb7 100644
--- a/tests/phpunit/tests/dependencies/scripts.php
+++ b/tests/phpunit/tests/dependencies/scripts.php
@@ -10,6 +10,7 @@ class Tests_Dependencies_Scripts extends WP_UnitTestCase {
 		parent::setUp();
 		$this->old_wp_scripts = isset( $GLOBALS['wp_scripts'] ) ? $GLOBALS['wp_scripts'] : null;
 		remove_action( 'wp_default_scripts', 'wp_default_scripts' );
+		remove_action( 'wp_default_scripts', 'wp_default_packages' );
 		$GLOBALS['wp_scripts']                  = new WP_Scripts();
 		$GLOBALS['wp_scripts']->default_version = get_bloginfo( 'version' );
 	}
diff --git a/tools/webpack/media.js b/tools/webpack/media.js
index adfe632218..9a9f126233 100644
--- a/tools/webpack/media.js
+++ b/tools/webpack/media.js
@@ -18,10 +18,9 @@ include_files = {
 const baseDir = path.join( __dirname, '../../' );
 
 module.exports = function( env = { environment: 'production', watch: false } ) {
-	const mode = env.environment;
 
 	const mediaConfig = {
-		mode,
+		mode: "production",
 		cache: true,
 		entry: Object.assign( admin_files, include_files ),
 		output: {