diff --git a/wp-includes/embed.php b/wp-includes/embed.php
index a2eff42657..e0f4bc937c 100644
--- a/wp-includes/embed.php
+++ b/wp-includes/embed.php
@@ -359,7 +359,25 @@ function wp_oembed_add_discovery_links() {
  * @since 4.4.0
  */
 function wp_oembed_add_host_js() {
-	wp_enqueue_script( 'wp-embed' );
+	add_filter( 'embed_oembed_html', 'wp_maybe_enqueue_oembed_host_js' );
+}
+
+/**
+ * Enqueue the wp-embed script if the provided oEmbed HTML contains a post embed.
+ *
+ * In order to only enqueue the wp-embed script on pages that actually contain post embeds, this function checks if the
+ * provided HTML contains post embed markup and if so enqueues the script so that it will get printed in the footer.
+ *
+ * @since 5.9.0
+ *
+ * @param string $html Embed markup.
+ * @return string Embed markup (without modifications).
+ */
+function wp_maybe_enqueue_oembed_host_js( $html ) {
+	if ( preg_match( '/<blockquote\s[^>]*wp-embedded-content/', $html ) ) {
+		wp_enqueue_script( 'wp-embed' );
+	}
+	return $html;
 }
 
 /**
@@ -450,33 +468,22 @@ function get_post_embed_html( $width, $height, $post = null ) {
 
 	$embed_url = get_post_embed_url( $post );
 
-	$output = '<blockquote class="wp-embedded-content"><a href="' . esc_url( get_permalink( $post ) ) . '">' . get_the_title( $post ) . "</a></blockquote>\n";
+	$secret     = wp_generate_password( 10, false );
+	$embed_url .= "#?secret={$secret}";
 
-	$output .= "<script type='text/javascript'>\n";
-	$output .= "<!--//--><![CDATA[//><!--\n";
-	if ( SCRIPT_DEBUG ) {
-		$output .= file_get_contents( ABSPATH . WPINC . '/js/wp-embed.js' );
-	} else {
-		/*
-		 * If you're looking at a src version of this file, you'll see an "include"
-		 * statement below. This is used by the `npm run build` process to directly
-		 * include a minified version of wp-embed.js, instead of using the
-		 * file_get_contents() method from above.
-		 *
-		 * If you're looking at a build version of this file, you'll see a string of
-		 * minified JavaScript. If you need to debug it, please turn on SCRIPT_DEBUG
-		 * and edit wp-embed.js directly.
-		 */
-		$output .= <<<JS
-		/*! This file is auto-generated */
-		!function(c,d){"use strict";var e=!1,n=!1;if(d.querySelector)if(c.addEventListener)e=!0;if(c.wp=c.wp||{},!c.wp.receiveEmbedMessage)if(c.wp.receiveEmbedMessage=function(e){var t=e.data;if(t)if(t.secret||t.message||t.value)if(!/[^a-zA-Z0-9]/.test(t.secret)){for(var r,a,i,s=d.querySelectorAll('iframe[data-secret="'+t.secret+'"]'),n=d.querySelectorAll('blockquote[data-secret="'+t.secret+'"]'),o=0;o<n.length;o++)n[o].style.display="none";for(o=0;o<s.length;o++)if(r=s[o],e.source===r.contentWindow){if(r.removeAttribute("style"),"height"===t.message){if(1e3<(i=parseInt(t.value,10)))i=1e3;else if(~~i<200)i=200;r.height=i}if("link"===t.message)if(a=d.createElement("a"),i=d.createElement("a"),a.href=r.getAttribute("src"),i.href=t.value,i.host===a.host)if(d.activeElement===r)c.top.location.href=t.value}}},e)c.addEventListener("message",c.wp.receiveEmbedMessage,!1),d.addEventListener("DOMContentLoaded",t,!1),c.addEventListener("load",t,!1);function t(){if(!n){n=!0;for(var e,t,r=-1!==navigator.appVersion.indexOf("MSIE 10"),a=!!navigator.userAgent.match(/Trident.*rv:11\./),i=d.querySelectorAll("iframe.wp-embedded-content"),s=0;s<i.length;s++){if(!(e=i[s]).getAttribute("data-secret"))t=Math.random().toString(36).substr(2,10),e.src+="#?secret="+t,e.setAttribute("data-secret",t);if(r||a)(t=e.cloneNode(!0)).removeAttribute("security"),e.parentNode.replaceChild(t,e)}}}}(window,document);
-JS;
-	}
-	$output .= "\n//--><!]]>";
-	$output .= "\n</script>";
+	$output = wp_get_inline_script_tag(
+		file_get_contents( sprintf( ABSPATH . WPINC . '/js/wp-embed' . wp_scripts_get_suffix() . '.js' ) )
+	);
 
 	$output .= sprintf(
-		'<iframe sandbox="allow-scripts" security="restricted" src="%1$s" width="%2$d" height="%3$d" title="%4$s" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" class="wp-embedded-content"></iframe>',
+		'<blockquote class="wp-embedded-content" data-secret="%1$s"><a href="%2$s">%3$s</a></blockquote>',
+		esc_attr( $secret ),
+		esc_url( get_permalink( $post ) ),
+		get_the_title( $post )
+	);
+
+	$output .= sprintf(
+		'<iframe sandbox="allow-scripts" security="restricted" src="%1$s" width="%2$d" height="%3$d" title="%4$s" data-secret="%5$s" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" class="wp-embedded-content"></iframe>',
 		esc_url( $embed_url ),
 		absint( $width ),
 		absint( $height ),
@@ -487,7 +494,8 @@ JS;
 				get_the_title( $post ),
 				get_bloginfo( 'name' )
 			)
-		)
+		),
+		esc_attr( $secret )
 	);
 
 	/**
@@ -1051,8 +1059,7 @@ function print_embed_styles() {
 		 * and edit wp-embed-template.css directly.
 		 */
 		?>
-			/*! This file is auto-generated */
-			body,html{padding:0;margin:0}body{font-family:sans-serif}.screen-reader-text{border:0;clip:rect(1px,1px,1px,1px);-webkit-clip-path:inset(50%);clip-path:inset(50%);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px;word-wrap:normal!important}.dashicons{display:inline-block;width:20px;height:20px;background-color:transparent;background-repeat:no-repeat;background-size:20px;background-position:center;transition:background .1s ease-in;position:relative;top:5px}.dashicons-no{background-image:url("data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%27http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%27%20viewBox%3D%270%200%2020%2020%27%3E%3Cpath%20d%3D%27M15.55%2013.7l-2.19%202.06-3.42-3.65-3.64%203.43-2.06-2.18%203.64-3.43-3.42-3.64%202.18-2.06%203.43%203.64%203.64-3.42%202.05%202.18-3.64%203.43z%27%20fill%3D%27%23fff%27%2F%3E%3C%2Fsvg%3E")}.dashicons-admin-comments{background-image:url("data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%27http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%27%20viewBox%3D%270%200%2020%2020%27%3E%3Cpath%20d%3D%27M5%202h9q.82%200%201.41.59T16%204v7q0%20.82-.59%201.41T14%2013h-2l-5%205v-5H5q-.82%200-1.41-.59T3%2011V4q0-.82.59-1.41T5%202z%27%20fill%3D%27%2382878c%27%2F%3E%3C%2Fsvg%3E")}.wp-embed-comments a:hover .dashicons-admin-comments{background-image:url("data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%27http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%27%20viewBox%3D%270%200%2020%2020%27%3E%3Cpath%20d%3D%27M5%202h9q.82%200%201.41.59T16%204v7q0%20.82-.59%201.41T14%2013h-2l-5%205v-5H5q-.82%200-1.41-.59T3%2011V4q0-.82.59-1.41T5%202z%27%20fill%3D%27%230073aa%27%2F%3E%3C%2Fsvg%3E")}.dashicons-share{background-image:url("data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%27http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%27%20viewBox%3D%270%200%2020%2020%27%3E%3Cpath%20d%3D%27M14.5%2012q1.24%200%202.12.88T17.5%2015t-.88%202.12-2.12.88-2.12-.88T11.5%2015q0-.34.09-.69l-4.38-2.3Q6.32%2013%205%2013q-1.24%200-2.12-.88T2%2010t.88-2.12T5%207q1.3%200%202.21.99l4.38-2.3q-.09-.35-.09-.69%200-1.24.88-2.12T14.5%202t2.12.88T17.5%205t-.88%202.12T14.5%208q-1.3%200-2.21-.99l-4.38%202.3Q8%209.66%208%2010t-.09.69l4.38%202.3q.89-.99%202.21-.99z%27%20fill%3D%27%2382878c%27%2F%3E%3C%2Fsvg%3E");display:none}.js .dashicons-share{display:inline-block}.wp-embed-share-dialog-open:hover .dashicons-share{background-image:url("data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%27http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%27%20viewBox%3D%270%200%2020%2020%27%3E%3Cpath%20d%3D%27M14.5%2012q1.24%200%202.12.88T17.5%2015t-.88%202.12-2.12.88-2.12-.88T11.5%2015q0-.34.09-.69l-4.38-2.3Q6.32%2013%205%2013q-1.24%200-2.12-.88T2%2010t.88-2.12T5%207q1.3%200%202.21.99l4.38-2.3q-.09-.35-.09-.69%200-1.24.88-2.12T14.5%202t2.12.88T17.5%205t-.88%202.12T14.5%208q-1.3%200-2.21-.99l-4.38%202.3Q8%209.66%208%2010t-.09.69l4.38%202.3q.89-.99%202.21-.99z%27%20fill%3D%27%230073aa%27%2F%3E%3C%2Fsvg%3E")}.wp-embed{padding:25px;font-size:14px;font-weight:400;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Oxygen-Sans,Ubuntu,Cantarell,"Helvetica Neue",sans-serif;line-height:1.5;color:#8c8f94;background:#fff;border:1px solid #dcdcde;box-shadow:0 1px 1px rgba(0,0,0,.05);overflow:auto;zoom:1}.wp-embed a{color:#8c8f94;text-decoration:none}.wp-embed a:hover{text-decoration:underline}.wp-embed-featured-image{margin-bottom:20px}.wp-embed-featured-image img{width:100%;height:auto;border:none}.wp-embed-featured-image.square{float:left;max-width:160px;margin-right:20px}.wp-embed p{margin:0}p.wp-embed-heading{margin:0 0 15px;font-weight:600;font-size:22px;line-height:1.3}.wp-embed-heading a{color:#2c3338}.wp-embed .wp-embed-more{color:#c3c4c7}.wp-embed-footer{display:table;width:100%;margin-top:30px}.wp-embed-site-icon{position:absolute;top:50%;left:0;transform:translateY(-50%);height:25px;width:25px;border:0}.wp-embed-site-title{font-weight:600;line-height:1.78571428}.wp-embed-site-title a{position:relative;display:inline-block;padding-left:35px}.wp-embed-meta,.wp-embed-site-title{display:table-cell}.wp-embed-meta{text-align:right;white-space:nowrap;vertical-align:middle}.wp-embed-comments,.wp-embed-share{display:inline}.wp-embed-meta a:hover{text-decoration:none;color:#2271b1}.wp-embed-comments a{line-height:1.78571428;display:inline-block}.wp-embed-comments+.wp-embed-share{margin-left:10px}.wp-embed-share-dialog{position:absolute;top:0;left:0;right:0;bottom:0;background-color:#1d2327;background-color:rgba(0,0,0,.9);color:#fff;opacity:1;transition:opacity .25s ease-in-out}.wp-embed-share-dialog.hidden{opacity:0;visibility:hidden}.wp-embed-share-dialog-close,.wp-embed-share-dialog-open{margin:-8px 0 0;padding:0;background:0 0;border:none;cursor:pointer;outline:0}.wp-embed-share-dialog-close .dashicons,.wp-embed-share-dialog-open .dashicons{padding:4px}.wp-embed-share-dialog-open .dashicons{top:8px}.wp-embed-share-dialog-close:focus .dashicons,.wp-embed-share-dialog-open:focus .dashicons{box-shadow:0 0 0 1px #4f94d4,0 0 2px 1px rgba(79,148,212,.8);border-radius:100%}.wp-embed-share-dialog-close{position:absolute;top:20px;right:20px;font-size:22px}.wp-embed-share-dialog-close:hover{text-decoration:none}.wp-embed-share-dialog-close .dashicons{height:24px;width:24px;background-size:24px}.wp-embed-share-dialog-content{height:100%;transform-style:preserve-3d;overflow:hidden}.wp-embed-share-dialog-text{margin-top:25px;padding:20px}.wp-embed-share-tabs{margin:0 0 20px;padding:0;list-style:none}.wp-embed-share-tab-button{display:inline-block}.wp-embed-share-tab-button button{margin:0;padding:0;border:none;background:0 0;font-size:16px;line-height:1.3;color:#a7aaad;cursor:pointer;transition:color .1s ease-in}.wp-embed-share-tab-button [aria-selected=true]{color:#fff}.wp-embed-share-tab-button button:hover{color:#fff}.wp-embed-share-tab-button+.wp-embed-share-tab-button{margin:0 0 0 10px;padding:0 0 0 11px;border-left:1px solid #a7aaad}.wp-embed-share-tab[aria-hidden=true]{display:none}p.wp-embed-share-description{margin:0;font-size:14px;line-height:1;font-style:italic;color:#a7aaad}.wp-embed-share-input{box-sizing:border-box;width:100%;border:none;height:28px;margin:0 0 10px;padding:0 5px;font-size:14px;font-weight:400;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Oxygen-Sans,Ubuntu,Cantarell,"Helvetica Neue",sans-serif;line-height:1.5;resize:none;cursor:text}textarea.wp-embed-share-input{height:72px}html[dir=rtl] .wp-embed-featured-image.square{float:right;margin-right:0;margin-left:20px}html[dir=rtl] .wp-embed-site-title a{padding-left:0;padding-right:35px}html[dir=rtl] .wp-embed-site-icon{margin-right:0;margin-left:10px;left:auto;right:0}html[dir=rtl] .wp-embed-meta{text-align:left}html[dir=rtl] .wp-embed-share{margin-left:0;margin-right:10px}html[dir=rtl] .wp-embed-share-dialog-close{right:auto;left:20px}html[dir=rtl] .wp-embed-share-tab-button+.wp-embed-share-tab-button{margin:0 10px 0 0;padding:0 11px 0 0;border-left:none;border-right:1px solid #a7aaad}
+			include "css/wp-embed-template.min.css"
 		<?php
 	}
 	?>
@@ -1084,8 +1091,7 @@ function print_embed_scripts() {
 		 * and edit wp-embed-template.js directly.
 		 */
 		?>
-			/*! This file is auto-generated */
-			!function(c,u){"use strict";var r,t,e,n=u.querySelector&&c.addEventListener,b=!1;function f(e,t){c.parent.postMessage({message:e,value:t,secret:r},"*")}function i(){if(!b){b=!0;var e,r=u.querySelector(".wp-embed-share-dialog"),t=u.querySelector(".wp-embed-share-dialog-open"),n=u.querySelector(".wp-embed-share-dialog-close"),i=u.querySelectorAll(".wp-embed-share-input"),a=u.querySelectorAll(".wp-embed-share-tab-button button"),o=u.querySelector(".wp-embed-featured-image img");if(i)for(e=0;e<i.length;e++)i[e].addEventListener("click",function(e){e.target.select()});if(t&&t.addEventListener("click",function(){r.className=r.className.replace("hidden",""),u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]').focus()}),n&&n.addEventListener("click",function(){l()}),a)for(e=0;e<a.length;e++)a[e].addEventListener("click",s),a[e].addEventListener("keydown",d);u.addEventListener("keydown",function(e){var t;27===e.keyCode&&-1===r.className.indexOf("hidden")?l():9===e.keyCode&&(t=e,e=u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]'),n!==t.target||t.shiftKey?e===t.target&&t.shiftKey&&(n.focus(),t.preventDefault()):(e.focus(),t.preventDefault()))},!1),c.self!==c.top&&(f("height",Math.ceil(u.body.getBoundingClientRect().height)),o&&o.addEventListener("load",function(){f("height",Math.ceil(u.body.getBoundingClientRect().height))}),u.addEventListener("click",function(e){var t=((t=e.target).hasAttribute("href")?t:t.parentElement).getAttribute("href");event.altKey||event.ctrlKey||event.metaKey||event.shiftKey||t&&(f("link",t),e.preventDefault())}))}function l(){r.className+=" hidden",u.querySelector(".wp-embed-share-dialog-open").focus()}function s(e){var t=u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]');t.setAttribute("aria-selected","false"),u.querySelector("#"+t.getAttribute("aria-controls")).setAttribute("aria-hidden","true"),e.target.setAttribute("aria-selected","true"),u.querySelector("#"+e.target.getAttribute("aria-controls")).setAttribute("aria-hidden","false")}function d(e){var t,r=e.target,n=r.parentElement.previousElementSibling,i=r.parentElement.nextElementSibling;if(37===e.keyCode)t=n;else{if(39!==e.keyCode)return!1;t=i}(t="rtl"===u.documentElement.getAttribute("dir")?t===n?i:n:t)&&(t=t.firstElementChild,r.setAttribute("tabindex","-1"),r.setAttribute("aria-selected",!1),u.querySelector("#"+r.getAttribute("aria-controls")).setAttribute("aria-hidden","true"),t.setAttribute("tabindex","0"),t.setAttribute("aria-selected","true"),t.focus(),u.querySelector("#"+t.getAttribute("aria-controls")).setAttribute("aria-hidden","false"))}}n&&(!function e(){c.self===c.top||r||(r=c.location.hash.replace(/.*secret=([\d\w]{10}).*/,"$1"),clearTimeout(t),t=setTimeout(function(){e()},100))}(),u.documentElement.className=u.documentElement.className.replace(/\bno-js\b/,"")+" js",u.addEventListener("DOMContentLoaded",i,!1),c.addEventListener("load",i,!1),c.addEventListener("resize",function(){c.self!==c.top&&(clearTimeout(e),e=setTimeout(function(){f("height",Math.ceil(u.body.getBoundingClientRect().height))},100))},!1))}(window,document);
+			include "js/wp-embed-template.min.js"
 		<?php
 	}
 	?>
diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index 91fcd44ced..38a4a113a9 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -5756,8 +5756,7 @@ function _print_emoji_detection_script() {
 		'svgExt'  => apply_filters( 'emoji_svg_ext', '.svg' ),
 	);
 
-	$version   = 'ver=' . get_bloginfo( 'version' );
-	$type_attr = current_theme_supports( 'html5', 'style' ) ? '' : ' type="text/javascript"';
+	$version = 'ver=' . get_bloginfo( 'version' );
 
 	if ( SCRIPT_DEBUG ) {
 		$settings['source'] = array(
@@ -5766,36 +5765,17 @@ function _print_emoji_detection_script() {
 			/** This filter is documented in wp-includes/class.wp-scripts.php */
 			'twemoji' => apply_filters( 'script_loader_src', includes_url( "js/twemoji.js?$version" ), 'twemoji' ),
 		);
-
-		?>
-		<script<?php echo $type_attr; ?>>
-			window._wpemojiSettings = <?php echo wp_json_encode( $settings ); ?>;
-			<?php readfile( ABSPATH . WPINC . '/js/wp-emoji-loader.js' ); ?>
-		</script>
-		<?php
 	} else {
 		$settings['source'] = array(
 			/** This filter is documented in wp-includes/class.wp-scripts.php */
 			'concatemoji' => apply_filters( 'script_loader_src', includes_url( "js/wp-emoji-release.min.js?$version" ), 'concatemoji' ),
 		);
-
-		/*
-		 * If you're looking at a src version of this file, you'll see an "include"
-		 * statement below. This is used by the `npm run build` process to directly
-		 * include a minified version of wp-emoji-loader.js, instead of using the
-		 * readfile() method from above.
-		 *
-		 * If you're looking at a build version of this file, you'll see a string of
-		 * minified JavaScript. If you need to debug it, please turn on SCRIPT_DEBUG
-		 * and edit wp-emoji-loader.js directly.
-		 */
-		?>
-		<script<?php echo $type_attr; ?>>
-			window._wpemojiSettings = <?php echo wp_json_encode( $settings ); ?>;
-			!function(e,a,t){var n,r,o,i=a.createElement("canvas"),p=i.getContext&&i.getContext("2d");function s(e,t){var a=String.fromCharCode;p.clearRect(0,0,i.width,i.height),p.fillText(a.apply(this,e),0,0);e=i.toDataURL();return p.clearRect(0,0,i.width,i.height),p.fillText(a.apply(this,t),0,0),e===i.toDataURL()}function c(e){var t=a.createElement("script");t.src=e,t.defer=t.type="text/javascript",a.getElementsByTagName("head")[0].appendChild(t)}for(o=Array("flag","emoji"),t.supports={everything:!0,everythingExceptFlag:!0},r=0;r<o.length;r++)t.supports[o[r]]=function(e){if(!p||!p.fillText)return!1;switch(p.textBaseline="top",p.font="600 32px Arial",e){case"flag":return s([127987,65039,8205,9895,65039],[127987,65039,8203,9895,65039])?!1:!s([55356,56826,55356,56819],[55356,56826,8203,55356,56819])&&!s([55356,57332,56128,56423,56128,56418,56128,56421,56128,56430,56128,56423,56128,56447],[55356,57332,8203,56128,56423,8203,56128,56418,8203,56128,56421,8203,56128,56430,8203,56128,56423,8203,56128,56447]);case"emoji":return!s([10084,65039,8205,55357,56613],[10084,65039,8203,55357,56613])}return!1}(o[r]),t.supports.everything=t.supports.everything&&t.supports[o[r]],"flag"!==o[r]&&(t.supports.everythingExceptFlag=t.supports.everythingExceptFlag&&t.supports[o[r]]);t.supports.everythingExceptFlag=t.supports.everythingExceptFlag&&!t.supports.flag,t.DOMReady=!1,t.readyCallback=function(){t.DOMReady=!0},t.supports.everything||(n=function(){t.readyCallback()},a.addEventListener?(a.addEventListener("DOMContentLoaded",n,!1),e.addEventListener("load",n,!1)):(e.attachEvent("onload",n),a.attachEvent("onreadystatechange",function(){"complete"===a.readyState&&t.readyCallback()})),(n=t.source||{}).concatemoji?c(n.concatemoji):n.wpemoji&&n.twemoji&&(c(n.twemoji),c(n.wpemoji)))}(window,document,window._wpemojiSettings);
-		</script>
-		<?php
 	}
+
+	wp_print_inline_script_tag(
+		sprintf( 'window._wpemojiSettings = %s;', wp_json_encode( $settings ) ) .
+			file_get_contents( sprintf( ABSPATH . WPINC . '/js/wp-emoji-loader' . wp_scripts_get_suffix() . '.js' ) )
+	);
 }
 
 /**
diff --git a/wp-includes/js/wp-embed-template.js b/wp-includes/js/wp-embed-template.js
index 86fb7d2c84..ae58e4e967 100644
--- a/wp-includes/js/wp-embed-template.js
+++ b/wp-includes/js/wp-embed-template.js
@@ -18,6 +18,13 @@
 		}, '*' );
 	}
 
+	/**
+	 * Send the height message to the parent window.
+	 */
+	function sendHeightMessage() {
+		sendEmbedMessage( 'height', Math.ceil( document.body.getBoundingClientRect().height ) );
+	}
+
 	function onLoad() {
 		if ( loaded ) {
 			return;
@@ -138,13 +145,11 @@
 		}
 
 		// Send this document's height to the parent (embedding) site.
-		sendEmbedMessage( 'height', Math.ceil( document.body.getBoundingClientRect().height ) );
+		sendHeightMessage();
 
 		// Send the document's height again after the featured image has been loaded.
 		if ( featured_image ) {
-			featured_image.addEventListener( 'load', function() {
-				sendEmbedMessage( 'height', Math.ceil( document.body.getBoundingClientRect().height ) );
-			} );
+			featured_image.addEventListener( 'load', sendHeightMessage );
 		}
 
 		/**
@@ -184,9 +189,36 @@
 
 		clearTimeout( resizing );
 
-		resizing = setTimeout( function () {
-			sendEmbedMessage( 'height', Math.ceil( document.body.getBoundingClientRect().height ) );
-		}, 100 );
+		resizing = setTimeout( sendHeightMessage, 100 );
+	}
+
+	/**
+	 * Message handler.
+	 *
+	 * @param {MessageEvent} event
+	 */
+	function onMessage( event ) {
+		var data = event.data;
+
+		if ( ! data ) {
+			return;
+		}
+
+		if ( event.source !== window.parent ) {
+			return;
+		}
+
+		if ( ! ( data.secret || data.message ) ) {
+			return;
+		}
+
+		if ( data.secret !== secret ) {
+			return;
+		}
+
+		if ( 'ready' === data.message ) {
+			sendHeightMessage();
+		}
 	}
 
 	/**
@@ -212,5 +244,6 @@
 		document.addEventListener( 'DOMContentLoaded', onLoad, false );
 		window.addEventListener( 'load', onLoad, false );
 		window.addEventListener( 'resize', onResize, false );
+		window.addEventListener( 'message', onMessage, false );
 	}
 })( window, document );
diff --git a/wp-includes/js/wp-embed-template.min.js b/wp-includes/js/wp-embed-template.min.js
index 583f83c45f..edb565bd9f 100644
--- a/wp-includes/js/wp-embed-template.min.js
+++ b/wp-includes/js/wp-embed-template.min.js
@@ -1,2 +1,2 @@
 /*! This file is auto-generated */
-!function(c,u){"use strict";var r,t,e,n=u.querySelector&&c.addEventListener,b=!1;function f(e,t){c.parent.postMessage({message:e,value:t,secret:r},"*")}function i(){if(!b){b=!0;var e,r=u.querySelector(".wp-embed-share-dialog"),t=u.querySelector(".wp-embed-share-dialog-open"),n=u.querySelector(".wp-embed-share-dialog-close"),i=u.querySelectorAll(".wp-embed-share-input"),a=u.querySelectorAll(".wp-embed-share-tab-button button"),o=u.querySelector(".wp-embed-featured-image img");if(i)for(e=0;e<i.length;e++)i[e].addEventListener("click",function(e){e.target.select()});if(t&&t.addEventListener("click",function(){r.className=r.className.replace("hidden",""),u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]').focus()}),n&&n.addEventListener("click",function(){l()}),a)for(e=0;e<a.length;e++)a[e].addEventListener("click",s),a[e].addEventListener("keydown",d);u.addEventListener("keydown",function(e){var t;27===e.keyCode&&-1===r.className.indexOf("hidden")?l():9===e.keyCode&&(t=e,e=u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]'),n!==t.target||t.shiftKey?e===t.target&&t.shiftKey&&(n.focus(),t.preventDefault()):(e.focus(),t.preventDefault()))},!1),c.self!==c.top&&(f("height",Math.ceil(u.body.getBoundingClientRect().height)),o&&o.addEventListener("load",function(){f("height",Math.ceil(u.body.getBoundingClientRect().height))}),u.addEventListener("click",function(e){var t=((t=e.target).hasAttribute("href")?t:t.parentElement).getAttribute("href");event.altKey||event.ctrlKey||event.metaKey||event.shiftKey||t&&(f("link",t),e.preventDefault())}))}function l(){r.className+=" hidden",u.querySelector(".wp-embed-share-dialog-open").focus()}function s(e){var t=u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]');t.setAttribute("aria-selected","false"),u.querySelector("#"+t.getAttribute("aria-controls")).setAttribute("aria-hidden","true"),e.target.setAttribute("aria-selected","true"),u.querySelector("#"+e.target.getAttribute("aria-controls")).setAttribute("aria-hidden","false")}function d(e){var t,r=e.target,n=r.parentElement.previousElementSibling,i=r.parentElement.nextElementSibling;if(37===e.keyCode)t=n;else{if(39!==e.keyCode)return!1;t=i}(t="rtl"===u.documentElement.getAttribute("dir")?t===n?i:n:t)&&(t=t.firstElementChild,r.setAttribute("tabindex","-1"),r.setAttribute("aria-selected",!1),u.querySelector("#"+r.getAttribute("aria-controls")).setAttribute("aria-hidden","true"),t.setAttribute("tabindex","0"),t.setAttribute("aria-selected","true"),t.focus(),u.querySelector("#"+t.getAttribute("aria-controls")).setAttribute("aria-hidden","false"))}}n&&(!function e(){c.self===c.top||r||(r=c.location.hash.replace(/.*secret=([\d\w]{10}).*/,"$1"),clearTimeout(t),t=setTimeout(function(){e()},100))}(),u.documentElement.className=u.documentElement.className.replace(/\bno-js\b/,"")+" js",u.addEventListener("DOMContentLoaded",i,!1),c.addEventListener("load",i,!1),c.addEventListener("resize",function(){c.self!==c.top&&(clearTimeout(e),e=setTimeout(function(){f("height",Math.ceil(u.body.getBoundingClientRect().height))},100))},!1))}(window,document);
\ No newline at end of file
+!function(c,u){"use strict";var r,t,e,a=u.querySelector&&c.addEventListener,f=!1;function b(e,t){c.parent.postMessage({message:e,value:t,secret:r},"*")}function m(){b("height",Math.ceil(u.body.getBoundingClientRect().height))}function n(){if(!f){f=!0;var e,r=u.querySelector(".wp-embed-share-dialog"),t=u.querySelector(".wp-embed-share-dialog-open"),a=u.querySelector(".wp-embed-share-dialog-close"),n=u.querySelectorAll(".wp-embed-share-input"),i=u.querySelectorAll(".wp-embed-share-tab-button button"),s=u.querySelector(".wp-embed-featured-image img");if(n)for(e=0;e<n.length;e++)n[e].addEventListener("click",function(e){e.target.select()});if(t&&t.addEventListener("click",function(){r.className=r.className.replace("hidden",""),u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]').focus()}),a&&a.addEventListener("click",function(){o()}),i)for(e=0;e<i.length;e++)i[e].addEventListener("click",d),i[e].addEventListener("keydown",l);u.addEventListener("keydown",function(e){var t;27===e.keyCode&&-1===r.className.indexOf("hidden")?o():9===e.keyCode&&(t=e,e=u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]'),a!==t.target||t.shiftKey?e===t.target&&t.shiftKey&&(a.focus(),t.preventDefault()):(e.focus(),t.preventDefault()))},!1),c.self!==c.top&&(m(),s&&s.addEventListener("load",m),u.addEventListener("click",function(e){var t=((t=e.target).hasAttribute("href")?t:t.parentElement).getAttribute("href");event.altKey||event.ctrlKey||event.metaKey||event.shiftKey||t&&(b("link",t),e.preventDefault())}))}function o(){r.className+=" hidden",u.querySelector(".wp-embed-share-dialog-open").focus()}function d(e){var t=u.querySelector('.wp-embed-share-tab-button [aria-selected="true"]');t.setAttribute("aria-selected","false"),u.querySelector("#"+t.getAttribute("aria-controls")).setAttribute("aria-hidden","true"),e.target.setAttribute("aria-selected","true"),u.querySelector("#"+e.target.getAttribute("aria-controls")).setAttribute("aria-hidden","false")}function l(e){var t,r=e.target,a=r.parentElement.previousElementSibling,n=r.parentElement.nextElementSibling;if(37===e.keyCode)t=a;else{if(39!==e.keyCode)return!1;t=n}(t="rtl"===u.documentElement.getAttribute("dir")?t===a?n:a:t)&&(t=t.firstElementChild,r.setAttribute("tabindex","-1"),r.setAttribute("aria-selected",!1),u.querySelector("#"+r.getAttribute("aria-controls")).setAttribute("aria-hidden","true"),t.setAttribute("tabindex","0"),t.setAttribute("aria-selected","true"),t.focus(),u.querySelector("#"+t.getAttribute("aria-controls")).setAttribute("aria-hidden","false"))}}a&&(!function e(){c.self===c.top||r||(r=c.location.hash.replace(/.*secret=([\d\w]{10}).*/,"$1"),clearTimeout(t),t=setTimeout(function(){e()},100))}(),u.documentElement.className=u.documentElement.className.replace(/\bno-js\b/,"")+" js",u.addEventListener("DOMContentLoaded",n,!1),c.addEventListener("load",n,!1),c.addEventListener("resize",function(){c.self!==c.top&&(clearTimeout(e),e=setTimeout(m,100))},!1),c.addEventListener("message",function(e){var t=e.data;t&&e.source===c.parent&&(t.secret||t.message)&&t.secret===r&&"ready"===t.message&&m()},!1))}(window,document);
\ No newline at end of file
diff --git a/wp-includes/js/wp-embed.js b/wp-includes/js/wp-embed.js
index 887c7483fb..fa2934f379 100644
--- a/wp-includes/js/wp-embed.js
+++ b/wp-includes/js/wp-embed.js
@@ -27,6 +27,11 @@
 		return;
 	}
 
+	/**
+	 * Receive embed message.
+	 *
+	 * @param {MessageEvent} e
+	 */
 	window.wp.receiveEmbedMessage = function( e ) {
 		var data = e.data;
 
@@ -102,9 +107,11 @@
 			iframeClone, i, source, secret;
 
 		for ( i = 0; i < iframes.length; i++ ) {
+			/** @var {IframeElement} */
 			source = iframes[ i ];
 
-			if ( ! source.getAttribute( 'data-secret' ) ) {
+			secret = source.getAttribute( 'data-secret' );
+			if ( ! secret ) {
 				/* Add secret to iframe */
 				secret = Math.random().toString( 36 ).substr( 2, 10 );
 				source.src += '#?secret=' + secret;
@@ -117,6 +124,16 @@
 				iframeClone.removeAttribute( 'security' );
 				source.parentNode.replaceChild( iframeClone, source );
 			}
+
+			/*
+			 * Let post embed window know that the parent is ready for receiving the height message, in case the iframe
+			 * loaded before wp-embed.js was loaded. When the ready message is received by the post embed window, the
+			 * window will then (re-)send the height message right away.
+			 */
+			source.contentWindow.postMessage( {
+				message: 'ready',
+				secret: secret
+			}, '*' );
 		}
 	}
 
diff --git a/wp-includes/js/wp-embed.min.js b/wp-includes/js/wp-embed.min.js
index 16e4c135cd..8970cec75a 100644
--- a/wp-includes/js/wp-embed.min.js
+++ b/wp-includes/js/wp-embed.min.js
@@ -1,2 +1,2 @@
 /*! This file is auto-generated */
-!function(c,d){"use strict";var e=!1,n=!1;if(d.querySelector)if(c.addEventListener)e=!0;if(c.wp=c.wp||{},!c.wp.receiveEmbedMessage)if(c.wp.receiveEmbedMessage=function(e){var t=e.data;if(t)if(t.secret||t.message||t.value)if(!/[^a-zA-Z0-9]/.test(t.secret)){for(var r,a,i,s=d.querySelectorAll('iframe[data-secret="'+t.secret+'"]'),n=d.querySelectorAll('blockquote[data-secret="'+t.secret+'"]'),o=0;o<n.length;o++)n[o].style.display="none";for(o=0;o<s.length;o++)if(r=s[o],e.source===r.contentWindow){if(r.removeAttribute("style"),"height"===t.message){if(1e3<(i=parseInt(t.value,10)))i=1e3;else if(~~i<200)i=200;r.height=i}if("link"===t.message)if(a=d.createElement("a"),i=d.createElement("a"),a.href=r.getAttribute("src"),i.href=t.value,i.host===a.host)if(d.activeElement===r)c.top.location.href=t.value}}},e)c.addEventListener("message",c.wp.receiveEmbedMessage,!1),d.addEventListener("DOMContentLoaded",t,!1),c.addEventListener("load",t,!1);function t(){if(!n){n=!0;for(var e,t,r=-1!==navigator.appVersion.indexOf("MSIE 10"),a=!!navigator.userAgent.match(/Trident.*rv:11\./),i=d.querySelectorAll("iframe.wp-embedded-content"),s=0;s<i.length;s++){if(!(e=i[s]).getAttribute("data-secret"))t=Math.random().toString(36).substr(2,10),e.src+="#?secret="+t,e.setAttribute("data-secret",t);if(r||a)(t=e.cloneNode(!0)).removeAttribute("security"),e.parentNode.replaceChild(t,e)}}}}(window,document);
\ No newline at end of file
+!function(c,d){"use strict";var e=!1,o=!1;if(d.querySelector)if(c.addEventListener)e=!0;if(c.wp=c.wp||{},!c.wp.receiveEmbedMessage)if(c.wp.receiveEmbedMessage=function(e){var t=e.data;if(t)if(t.secret||t.message||t.value)if(!/[^a-zA-Z0-9]/.test(t.secret)){for(var r,a,i,s=d.querySelectorAll('iframe[data-secret="'+t.secret+'"]'),n=d.querySelectorAll('blockquote[data-secret="'+t.secret+'"]'),o=0;o<n.length;o++)n[o].style.display="none";for(o=0;o<s.length;o++)if(r=s[o],e.source===r.contentWindow){if(r.removeAttribute("style"),"height"===t.message){if(1e3<(i=parseInt(t.value,10)))i=1e3;else if(~~i<200)i=200;r.height=i}if("link"===t.message)if(a=d.createElement("a"),i=d.createElement("a"),a.href=r.getAttribute("src"),i.href=t.value,i.host===a.host)if(d.activeElement===r)c.top.location.href=t.value}}},e)c.addEventListener("message",c.wp.receiveEmbedMessage,!1),d.addEventListener("DOMContentLoaded",t,!1),c.addEventListener("load",t,!1);function t(){if(!o){o=!0;for(var e,t,r,a=-1!==navigator.appVersion.indexOf("MSIE 10"),i=!!navigator.userAgent.match(/Trident.*rv:11\./),s=d.querySelectorAll("iframe.wp-embedded-content"),n=0;n<s.length;n++){if(!(r=(t=s[n]).getAttribute("data-secret")))r=Math.random().toString(36).substr(2,10),t.src+="#?secret="+r,t.setAttribute("data-secret",r);if(a||i)(e=t.cloneNode(!0)).removeAttribute("security"),t.parentNode.replaceChild(e,t);t.contentWindow.postMessage({message:"ready",secret:r},"*")}}}}(window,document);
\ No newline at end of file
diff --git a/wp-includes/script-loader.php b/wp-includes/script-loader.php
index 00f9a15576..7463b0de36 100644
--- a/wp-includes/script-loader.php
+++ b/wp-includes/script-loader.php
@@ -1247,7 +1247,7 @@ function wp_default_scripts( $scripts ) {
 		)
 	);
 
-	$scripts->add( 'wp-embed', "/wp-includes/js/wp-embed$suffix.js" );
+	$scripts->add( 'wp-embed', "/wp-includes/js/wp-embed$suffix.js", array(), false, 1 );
 
 	// To enqueue media-views or media-editor, call wp_enqueue_media().
 	// Both rely on numerous settings, styles, and templates to operate correctly.
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 0889fef30a..82cac756bc 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52131';
+$wp_version = '5.9-alpha-52132';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.