diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index e56683da1b..bb892b564e 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -740,7 +740,6 @@ final class WP_Customize_Manager {
 		wp_enqueue_script( 'customize-preview' );
 		add_action( 'wp', array( $this, 'customize_preview_override_404_status' ) );
 		add_action( 'wp_head', array( $this, 'customize_preview_base' ) );
-		add_action( 'wp_head', array( $this, 'customize_preview_html5' ) );
 		add_action( 'wp_head', array( $this, 'customize_preview_loading_style' ) );
 		add_action( 'wp_footer', array( $this, 'customize_preview_settings' ), 20 );
 		add_action( 'shutdown', array( $this, 'customize_preview_signature' ), 1000 );
@@ -787,18 +786,10 @@ final class WP_Customize_Manager {
 	 * Print a workaround to handle HTML5 tags in IE < 9.
 	 *
 	 * @since 3.4.0
+	 * @deprecated 4.7.0 Customizer no longer supports IE8, so all supported browsers recognize HTML5.
 	 */
-	public function customize_preview_html5() { ?>
-		<!--[if lt IE 9]>
-		<script type="text/javascript">
-			var e = [ 'abbr', 'article', 'aside', 'audio', 'canvas', 'datalist', 'details',
-				'figure', 'footer', 'header', 'hgroup', 'mark', 'menu', 'meter', 'nav',
-				'output', 'progress', 'section', 'time', 'video' ];
-			for ( var i = 0; i < e.length; i++ ) {
-				document.createElement( e[i] );
-			}
-		</script>
-		<![endif]--><?php
+	public function customize_preview_html5() {
+		_deprecated_function( __FUNCTION__, '4.7.0' );
 	}
 
 	/**
diff --git a/wp-includes/js/customize-selective-refresh.js b/wp-includes/js/customize-selective-refresh.js
index ec51058ec4..6bab103ff9 100644
--- a/wp-includes/js/customize-selective-refresh.js
+++ b/wp-includes/js/customize-selective-refresh.js
@@ -745,11 +745,6 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 	api.bind( 'preview-ready', function() {
 		var handleSettingChange, watchSettingChange, unwatchSettingChange;
 
-		// Polyfill for IE8 to support the document.head attribute.
-		if ( ! document.head ) {
-			document.head = $( 'head:first' )[0];
-		}
-
 		_.extend( self.data, _customizePartialRefreshExports );
 
 		// Create the partial JS models.
diff --git a/wp-includes/js/customize-selective-refresh.min.js b/wp-includes/js/customize-selective-refresh.min.js
index 52d4f5251d..f45be9d430 100644
--- a/wp-includes/js/customize-selective-refresh.min.js
+++ b/wp-includes/js/customize-selective-refresh.min.js
@@ -1 +1 @@
-wp.customize.selectiveRefresh=function(a,b){"use strict";var c,d,e;return c={ready:a.Deferred(),data:{partials:{},renderQueryVar:"",l10n:{shiftClickToEdit:""},refreshBuffer:250},currentRequest:null},_.extend(c,b.Events),d=c.Partial=b.Class.extend({id:null,initialize:function(b,c){var d=this;c=c||{},d.id=b,d.params=_.extend({selector:null,settings:[],primarySetting:null,containerInclusive:!1,fallbackRefresh:!0},c.params||{}),d.deferred={},d.deferred.ready=a.Deferred(),d.deferred.ready.done(function(){d.ready()})},ready:function(){var b=this;_.each(_.pluck(b.placements(),"container"),function(b){a(b).attr("title",c.data.l10n.shiftClickToEdit)}),a(document).on("click",b.params.selector,function(c){c.shiftKey&&(c.preventDefault(),_.each(b.placements(),function(d){a(d.container).is(c.currentTarget)&&b.showControl()}))})},placements:function(){var b,c=this;return b=c.params.selector||"",b&&(b+=", "),b+='[data-customize-partial-id="'+c.id+'"]',a(b).map(function(){var b,d=a(this);if(b=d.data("customize-partial-placement-context"),_.isString(b)&&"{"===b.substr(0,1))throw new Error("context JSON parse error");return new e({partial:c,container:d,context:b})}).get()},settings:function(){var a=this;return a.params.settings&&0!==a.params.settings.length?a.params.settings:a.params.primarySetting?[a.params.primarySetting]:[a.id]},isRelatedSetting:function(a){var c=this;return _.isString(a)&&(a=b(a)),a?-1!==_.indexOf(c.settings(),a.id):!1},showControl:function(){var a=this,c=a.params.primarySetting;c||(c=_.first(a.settings())),b.preview.send("focus-control-for-setting",c)},preparePlacement:function(b){a(b.container).addClass("customize-partial-refreshing")},_pendingRefreshPromise:null,refresh:function(){var a,b=this;return a=c.requestPartial(b),b._pendingRefreshPromise||(_.each(b.placements(),function(a){b.preparePlacement(a)}),a.done(function(a){_.each(a,function(a){b.renderContent(a)})}),a.fail(function(a,c){b.fallback(a,c)}),b._pendingRefreshPromise=a,a.always(function(){b._pendingRefreshPromise=null})),a},renderContent:function(b){var d,e,f=this;if(!b.container)return f.fallback(new Error("no_container"),[b]),!1;if(b.container=a(b.container),!1===b.addedContent)return f.fallback(new Error("missing_render"),[b]),!1;if(!_.isString(b.addedContent))return f.fallback(new Error("non_string_content"),[b]),!1;c.orginalDocumentWrite=document.write,document.write=function(){throw new Error(c.data.l10n.badDocumentWrite)};try{if(d=b.addedContent,wp.emoji&&wp.emoji.parse&&!a.contains(document.head,b.container[0])&&(d=wp.emoji.parse(d)),f.params.containerInclusive)e=a(d),b.context=_.extend(b.context,e.data("customize-partial-placement-context")||{}),e.data("customize-partial-placement-context",b.context),b.removedNodes=b.container,b.container=e,b.removedNodes.replaceWith(b.container),b.container.attr("title",c.data.l10n.shiftClickToEdit);else{for(b.removedNodes=document.createDocumentFragment();b.container[0].firstChild;)b.removedNodes.appendChild(b.container[0].firstChild);b.container.html(d)}b.container.removeClass("customize-render-content-error")}catch(g){"undefined"!=typeof console&&console.error&&console.error(f.id,g)}return document.write=c.orginalDocumentWrite,c.orginalDocumentWrite=null,b.container.removeClass("customize-partial-refreshing"),b.container.data("customize-partial-content-rendered",!0),c.trigger("partial-content-rendered",b),!0},fallback:function(){var a=this;a.params.fallbackRefresh&&c.requestFullRefresh()}}),c.Placement=e=b.Class.extend({partial:null,container:null,startNode:null,endNode:null,context:null,addedContent:null,removedNodes:null,initialize:function(b){var c=this;if(b=_.extend({},b||{}),!b.partial||!b.partial.extended(d))throw new Error("Missing partial");b.context=b.context||{},b.container&&(b.container=a(b.container)),_.extend(c,b)}}),c.partialConstructor={},c.partial=new b.Values({defaultConstructor:d}),c.getCustomizeQuery=function(){var a={};return b.each(function(b,c){b._dirty&&(a[c]=b())}),{wp_customize:"on",nonce:b.settings.nonce.preview,theme:b.settings.theme.stylesheet,customized:JSON.stringify(a)}},c._pendingPartialRequests={},c._debouncedTimeoutId=null,c._currentRequest=null,c.requestFullRefresh=function(){b.preview.send("refresh")},c.requestPartial=function(d){var f;return c._debouncedTimeoutId&&(clearTimeout(c._debouncedTimeoutId),c._debouncedTimeoutId=null),c._currentRequest&&(c._currentRequest.abort(),c._currentRequest=null),f=c._pendingPartialRequests[d.id],f&&"pending"===f.deferred.state()||(f={deferred:a.Deferred(),partial:d},c._pendingPartialRequests[d.id]=f),d=null,c._debouncedTimeoutId=setTimeout(function(){var a,d,f,g;c._debouncedTimeoutId=null,a=c.getCustomizeQuery(),f={},d={},_.each(c._pendingPartialRequests,function(a,b){f[b]=a.partial.placements(),c.partial.has(b)?d[b]=_.map(f[b],function(a){return a.context||{}}):a.deferred.rejectWith(a.partial,[new Error("partial_removed"),f[b]])}),a.partials=JSON.stringify(d),a[c.data.renderQueryVar]="1",g=c._currentRequest=wp.ajax.send(null,{data:a,url:b.settings.url.self}),g.done(function(a){c.trigger("render-partials-response",a),a.errors&&"undefined"!=typeof console&&console.warn&&_.each(a.errors,function(a){console.warn(a)}),_.each(c._pendingPartialRequests,function(b,c){var d;_.isArray(a.contents[c])?(d=_.map(a.contents[c],function(a,d){var g=f[c][d];return g?g.addedContent=a:g=new e({partial:b.partial,addedContent:a}),g}),b.deferred.resolveWith(b.partial,[d])):b.deferred.rejectWith(b.partial,[new Error("unrecognized_partial"),f[c]])}),c._pendingPartialRequests={}}),g.fail(function(a,b){"abort"!==b&&(_.each(c._pendingPartialRequests,function(b,c){b.deferred.rejectWith(b.partial,[a,f[c]])}),c._pendingPartialRequests={})})},c.data.refreshBuffer),f.deferred.promise()},c.addPartials=function(b,d){var f;b||(b=document.documentElement),b=a(b),d=_.extend({triggerRendered:!0},d||{}),f=b.find("[data-customize-partial-id]"),b.is("[data-customize-partial-id]")&&(f=f.add(b)),f.each(function(){var b,f,g,h,i,j=a(this);f=j.data("customize-partial-id"),f&&(i=j.data("customize-partial-placement-context")||{},b=c.partial(f),b||(h=j.data("customize-partial-options")||{},h.constructingContainerContext=j.data("customize-partial-placement-context")||{},g=c.partialConstructor[j.data("customize-partial-type")]||c.Partial,b=new g(f,h),c.partial.add(b.id,b)),d.triggerRendered&&!j.data("customize-partial-content-rendered")&&c.trigger("partial-content-rendered",new e({partial:b,context:i,container:j})),j.data("customize-partial-content-rendered",!0))})},b.bind("preview-ready",function(){var d,e,f;document.head||(document.head=a("head:first")[0]),_.extend(c.data,_customizePartialRefreshExports),_.each(c.data.partials,function(a,b){var d,e=c.partial(b);e?_.extend(e.params,a):(d=c.partialConstructor[a.type]||c.Partial,e=new d(b,{params:a}),c.partial.add(b,e))}),d=function(a,b){var d=this;c.partial.each(function(c){c.isRelatedSetting(d,a,b)&&c.refresh()})},e=function(a){d.call(a,a(),null),a.bind(d)},f=function(a){d.call(a,null,a()),a.unbind(d)},b.bind("add",e),b.bind("remove",f),b.each(function(a){a.bind(d)}),c.addPartials(document.documentElement,{triggerRendered:!1}),"undefined"!=typeof MutationObserver&&(c.mutationObserver=new MutationObserver(function(b){_.each(b,function(b){c.addPartials(a(b.target))})}),c.mutationObserver.observe(document.documentElement,{childList:!0,subtree:!0})),b.selectiveRefresh.bind("partial-content-rendered",function(a){a.container&&c.addPartials(a.container)}),b.selectiveRefresh.bind("render-partials-response",function(a){a.setting_validities&&b.preview.send("selective-refresh-setting-validities",a.setting_validities)}),b.preview.bind("active",function(){c.partial.each(function(a){a.deferred.ready.resolve()}),c.partial.bind("add",function(a){a.deferred.ready.resolve()})})}),c}(jQuery,wp.customize);
\ No newline at end of file
+wp.customize.selectiveRefresh=function(a,b){"use strict";var c,d,e;return c={ready:a.Deferred(),data:{partials:{},renderQueryVar:"",l10n:{shiftClickToEdit:""},refreshBuffer:250},currentRequest:null},_.extend(c,b.Events),d=c.Partial=b.Class.extend({id:null,initialize:function(b,c){var d=this;c=c||{},d.id=b,d.params=_.extend({selector:null,settings:[],primarySetting:null,containerInclusive:!1,fallbackRefresh:!0},c.params||{}),d.deferred={},d.deferred.ready=a.Deferred(),d.deferred.ready.done(function(){d.ready()})},ready:function(){var b=this;_.each(_.pluck(b.placements(),"container"),function(b){a(b).attr("title",c.data.l10n.shiftClickToEdit)}),a(document).on("click",b.params.selector,function(c){c.shiftKey&&(c.preventDefault(),_.each(b.placements(),function(d){a(d.container).is(c.currentTarget)&&b.showControl()}))})},placements:function(){var b,c=this;return b=c.params.selector||"",b&&(b+=", "),b+='[data-customize-partial-id="'+c.id+'"]',a(b).map(function(){var b,d=a(this);if(b=d.data("customize-partial-placement-context"),_.isString(b)&&"{"===b.substr(0,1))throw new Error("context JSON parse error");return new e({partial:c,container:d,context:b})}).get()},settings:function(){var a=this;return a.params.settings&&0!==a.params.settings.length?a.params.settings:a.params.primarySetting?[a.params.primarySetting]:[a.id]},isRelatedSetting:function(a){var c=this;return _.isString(a)&&(a=b(a)),a?-1!==_.indexOf(c.settings(),a.id):!1},showControl:function(){var a=this,c=a.params.primarySetting;c||(c=_.first(a.settings())),b.preview.send("focus-control-for-setting",c)},preparePlacement:function(b){a(b.container).addClass("customize-partial-refreshing")},_pendingRefreshPromise:null,refresh:function(){var a,b=this;return a=c.requestPartial(b),b._pendingRefreshPromise||(_.each(b.placements(),function(a){b.preparePlacement(a)}),a.done(function(a){_.each(a,function(a){b.renderContent(a)})}),a.fail(function(a,c){b.fallback(a,c)}),b._pendingRefreshPromise=a,a.always(function(){b._pendingRefreshPromise=null})),a},renderContent:function(b){var d,e,f=this;if(!b.container)return f.fallback(new Error("no_container"),[b]),!1;if(b.container=a(b.container),!1===b.addedContent)return f.fallback(new Error("missing_render"),[b]),!1;if(!_.isString(b.addedContent))return f.fallback(new Error("non_string_content"),[b]),!1;c.orginalDocumentWrite=document.write,document.write=function(){throw new Error(c.data.l10n.badDocumentWrite)};try{if(d=b.addedContent,wp.emoji&&wp.emoji.parse&&!a.contains(document.head,b.container[0])&&(d=wp.emoji.parse(d)),f.params.containerInclusive)e=a(d),b.context=_.extend(b.context,e.data("customize-partial-placement-context")||{}),e.data("customize-partial-placement-context",b.context),b.removedNodes=b.container,b.container=e,b.removedNodes.replaceWith(b.container),b.container.attr("title",c.data.l10n.shiftClickToEdit);else{for(b.removedNodes=document.createDocumentFragment();b.container[0].firstChild;)b.removedNodes.appendChild(b.container[0].firstChild);b.container.html(d)}b.container.removeClass("customize-render-content-error")}catch(g){"undefined"!=typeof console&&console.error&&console.error(f.id,g)}return document.write=c.orginalDocumentWrite,c.orginalDocumentWrite=null,b.container.removeClass("customize-partial-refreshing"),b.container.data("customize-partial-content-rendered",!0),c.trigger("partial-content-rendered",b),!0},fallback:function(){var a=this;a.params.fallbackRefresh&&c.requestFullRefresh()}}),c.Placement=e=b.Class.extend({partial:null,container:null,startNode:null,endNode:null,context:null,addedContent:null,removedNodes:null,initialize:function(b){var c=this;if(b=_.extend({},b||{}),!b.partial||!b.partial.extended(d))throw new Error("Missing partial");b.context=b.context||{},b.container&&(b.container=a(b.container)),_.extend(c,b)}}),c.partialConstructor={},c.partial=new b.Values({defaultConstructor:d}),c.getCustomizeQuery=function(){var a={};return b.each(function(b,c){b._dirty&&(a[c]=b())}),{wp_customize:"on",nonce:b.settings.nonce.preview,theme:b.settings.theme.stylesheet,customized:JSON.stringify(a)}},c._pendingPartialRequests={},c._debouncedTimeoutId=null,c._currentRequest=null,c.requestFullRefresh=function(){b.preview.send("refresh")},c.requestPartial=function(d){var f;return c._debouncedTimeoutId&&(clearTimeout(c._debouncedTimeoutId),c._debouncedTimeoutId=null),c._currentRequest&&(c._currentRequest.abort(),c._currentRequest=null),f=c._pendingPartialRequests[d.id],f&&"pending"===f.deferred.state()||(f={deferred:a.Deferred(),partial:d},c._pendingPartialRequests[d.id]=f),d=null,c._debouncedTimeoutId=setTimeout(function(){var a,d,f,g;c._debouncedTimeoutId=null,a=c.getCustomizeQuery(),f={},d={},_.each(c._pendingPartialRequests,function(a,b){f[b]=a.partial.placements(),c.partial.has(b)?d[b]=_.map(f[b],function(a){return a.context||{}}):a.deferred.rejectWith(a.partial,[new Error("partial_removed"),f[b]])}),a.partials=JSON.stringify(d),a[c.data.renderQueryVar]="1",g=c._currentRequest=wp.ajax.send(null,{data:a,url:b.settings.url.self}),g.done(function(a){c.trigger("render-partials-response",a),a.errors&&"undefined"!=typeof console&&console.warn&&_.each(a.errors,function(a){console.warn(a)}),_.each(c._pendingPartialRequests,function(b,c){var d;_.isArray(a.contents[c])?(d=_.map(a.contents[c],function(a,d){var g=f[c][d];return g?g.addedContent=a:g=new e({partial:b.partial,addedContent:a}),g}),b.deferred.resolveWith(b.partial,[d])):b.deferred.rejectWith(b.partial,[new Error("unrecognized_partial"),f[c]])}),c._pendingPartialRequests={}}),g.fail(function(a,b){"abort"!==b&&(_.each(c._pendingPartialRequests,function(b,c){b.deferred.rejectWith(b.partial,[a,f[c]])}),c._pendingPartialRequests={})})},c.data.refreshBuffer),f.deferred.promise()},c.addPartials=function(b,d){var f;b||(b=document.documentElement),b=a(b),d=_.extend({triggerRendered:!0},d||{}),f=b.find("[data-customize-partial-id]"),b.is("[data-customize-partial-id]")&&(f=f.add(b)),f.each(function(){var b,f,g,h,i,j=a(this);f=j.data("customize-partial-id"),f&&(i=j.data("customize-partial-placement-context")||{},b=c.partial(f),b||(h=j.data("customize-partial-options")||{},h.constructingContainerContext=j.data("customize-partial-placement-context")||{},g=c.partialConstructor[j.data("customize-partial-type")]||c.Partial,b=new g(f,h),c.partial.add(b.id,b)),d.triggerRendered&&!j.data("customize-partial-content-rendered")&&c.trigger("partial-content-rendered",new e({partial:b,context:i,container:j})),j.data("customize-partial-content-rendered",!0))})},b.bind("preview-ready",function(){var d,e,f;_.extend(c.data,_customizePartialRefreshExports),_.each(c.data.partials,function(a,b){var d,e=c.partial(b);e?_.extend(e.params,a):(d=c.partialConstructor[a.type]||c.Partial,e=new d(b,{params:a}),c.partial.add(b,e))}),d=function(a,b){var d=this;c.partial.each(function(c){c.isRelatedSetting(d,a,b)&&c.refresh()})},e=function(a){d.call(a,a(),null),a.bind(d)},f=function(a){d.call(a,null,a()),a.unbind(d)},b.bind("add",e),b.bind("remove",f),b.each(function(a){a.bind(d)}),c.addPartials(document.documentElement,{triggerRendered:!1}),"undefined"!=typeof MutationObserver&&(c.mutationObserver=new MutationObserver(function(b){_.each(b,function(b){c.addPartials(a(b.target))})}),c.mutationObserver.observe(document.documentElement,{childList:!0,subtree:!0})),b.selectiveRefresh.bind("partial-content-rendered",function(a){a.container&&c.addPartials(a.container)}),b.selectiveRefresh.bind("render-partials-response",function(a){a.setting_validities&&b.preview.send("selective-refresh-setting-validities",a.setting_validities)}),b.preview.bind("active",function(){c.partial.each(function(a){a.deferred.ready.resolve()}),c.partial.bind("add",function(a){a.deferred.ready.resolve()})})}),c}(jQuery,wp.customize);
\ No newline at end of file
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 8592ee50cf..c8cf03fe6a 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -2151,6 +2151,7 @@ function wp_customize_url( $stylesheet = null ) {
  * to the body tag by default.
  *
  * @since 3.4.0
+ * @since 4.7.0 Support for IE8 and below is explicitly removed via conditional comments.
  */
 function wp_customize_support_script() {
 	$admin_origin = parse_url( admin_url() );
@@ -2158,20 +2159,28 @@ function wp_customize_support_script() {
 	$cross_domain = ( strtolower( $admin_origin[ 'host' ] ) != strtolower( $home_origin[ 'host' ] ) );
 
 	?>
-	<script type="text/javascript">
-		(function() {
-			var request, b = document.body, c = 'className', cs = 'customize-support', rcs = new RegExp('(^|\\s+)(no-)?'+cs+'(\\s+|$)');
+	<!--[if lte IE 8]>
+		<script type="text/javascript">
+			document.body.className = document.body.className.replace( /(^|\s)(no-)?customize-support(?=\s|$)/, '' ) + ' no-customize-support';
+		</script>
+	<![endif]-->
+	<!--[if gte IE 9]><!-->
+		<script type="text/javascript">
+			(function() {
+				var request, b = document.body, c = 'className', cs = 'customize-support', rcs = new RegExp('(^|\\s+)(no-)?'+cs+'(\\s+|$)');
 
-<?php		if ( $cross_domain ): ?>
-			request = (function(){ var xhr = new XMLHttpRequest(); return ('withCredentials' in xhr); })();
-<?php		else: ?>
-			request = true;
-<?php		endif; ?>
+		<?php	if ( $cross_domain ) : ?>
+				request = (function(){ var xhr = new XMLHttpRequest(); return ('withCredentials' in xhr); })();
+		<?php	else : ?>
+				request = true;
+		<?php	endif; ?>
 
-			b[c] = b[c].replace( rcs, ' ' );
-			b[c] += ( window.postMessage && request && Array.prototype.indexOf ? ' ' : ' no-' ) + cs;
-		}());
-	</script>
+				b[c] = b[c].replace( rcs, ' ' );
+				// The customizer requires postMessage and CORS (if the site is cross domain)
+				b[c] += ( window.postMessage && request ? ' ' : ' no-' ) + cs;
+			}());
+		</script>
+	<!--<![endif]-->
 	<?php
 }
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b2aa0672a3..b18435abc4 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-alpha-38648';
+$wp_version = '4.7-alpha-38649';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.