diff --git a/app/assets/javascripts/discourse/app/index.html b/app/assets/javascripts/discourse/app/index.html
index ba049ba54ce..0dde7cb0ab4 100644
--- a/app/assets/javascripts/discourse/app/index.html
+++ b/app/assets/javascripts/discourse/app/index.html
@@ -11,8 +11,10 @@
     <bootstrap-content key="before-script-load">
     {{content-for "before-script-load"}}
 
-    <script src="{{rootURL}}assets/vendor.js"></script>
-    <script src="{{rootURL}}assets/discourse.js"></script>
+    <script defer src="{{rootURL}}assets/vendor.js"></script>
+    <script defer src="{{rootURL}}assets/discourse.js"></script>
+
+    <ember-auto-import-scripts defer entrypoint="app"></ember-auto-import-scripts>
 
     <bootstrap-content key="head">
     {{content-for "head"}}
@@ -27,7 +29,7 @@
     <bootstrap-content key="hidden-login-form">
     <bootstrap-content key="preloaded">
 
-    <script src="{{rootURL}}assets/start-discourse.js"></script>
+    <script defer src="{{rootURL}}assets/start-discourse.js"></script>
 
     <bootstrap-content key="body-footer">
     {{content-for "body-footer"}}
diff --git a/app/assets/javascripts/discourse/ember-cli-build.js b/app/assets/javascripts/discourse/ember-cli-build.js
index d9232652ab8..7065afc5573 100644
--- a/app/assets/javascripts/discourse/ember-cli-build.js
+++ b/app/assets/javascripts/discourse/ember-cli-build.js
@@ -29,6 +29,7 @@ module.exports = function (defaults) {
     },
     autoImport: {
       forbidEval: true,
+      insertScriptsAt: "ember-auto-import-scripts",
     },
     fingerprint: {
       // Handled by Rails asset pipeline
diff --git a/app/assets/javascripts/discourse/lib/bootstrap-json/index.js b/app/assets/javascripts/discourse/lib/bootstrap-json/index.js
index a1fcc954366..46c891ecc6a 100644
--- a/app/assets/javascripts/discourse/lib/bootstrap-json/index.js
+++ b/app/assets/javascripts/discourse/lib/bootstrap-json/index.js
@@ -89,7 +89,7 @@ function head(buffer, bootstrap, headers, baseURL) {
     let { admin, staff } = user;
 
     if (staff) {
-      buffer.push(`<script src="${baseURL}assets/admin.js"></script>`);
+      buffer.push(`<script defer src="${baseURL}assets/admin.js"></script>`);
     }
 
     if (admin) {
@@ -98,7 +98,7 @@ function head(buffer, bootstrap, headers, baseURL) {
   }
 
   bootstrap.plugin_js.forEach((src) =>
-    buffer.push(`<script src="${src}"></script>`)
+    buffer.push(`<script defer src="${src}"></script>`)
   );
 
   buffer.push(bootstrap.theme_html.translations);
@@ -108,14 +108,14 @@ function head(buffer, bootstrap, headers, baseURL) {
 }
 
 function localeScript(buffer, bootstrap) {
-  buffer.push(`<script src="${bootstrap.locale_script}"></script>`);
+  buffer.push(`<script defer src="${bootstrap.locale_script}"></script>`);
 }
 
 function beforeScriptLoad(buffer, bootstrap) {
   buffer.push(bootstrap.html.before_script_load);
   localeScript(buffer, bootstrap);
   (bootstrap.extra_locales || []).forEach((l) =>
-    buffer.push(`<script src="${l}"></script>`)
+    buffer.push(`<script defer src="${l}"></script>`)
   );
 }
 
diff --git a/app/assets/javascripts/discourse/tests/index.html b/app/assets/javascripts/discourse/tests/index.html
index cc64b777149..8917097f05c 100644
--- a/app/assets/javascripts/discourse/tests/index.html
+++ b/app/assets/javascripts/discourse/tests/index.html
@@ -46,7 +46,9 @@
 
     <script src="/testem.js" integrity=""></script>
     <script src="{{rootURL}}assets/vendor.js"></script>
+    <ember-auto-import-scripts entrypoint="app"></ember-auto-import-scripts>
     <script src="{{rootURL}}assets/test-support.js"></script>
+    <ember-auto-import-scripts entrypoint="tests"></ember-auto-import-scripts>
     <script src="{{rootURL}}assets/discourse.js"></script>
     <script src="{{rootURL}}assets/discourse-markdown.js"></script>
     <script src="{{rootURL}}assets/admin.js"></script>
diff --git a/app/assets/javascripts/discourse/tests/test_starter.js b/app/assets/javascripts/discourse/tests/test_starter.js
index 0ab61639ba7..067e890fc16 100644
--- a/app/assets/javascripts/discourse/tests/test_starter.js
+++ b/app/assets/javascripts/discourse/tests/test_starter.js
@@ -1,10 +1,11 @@
 // discourse-skip-module
 
-document.write(
-  '<div id="ember-testing-container"><div id="ember-testing"></div></div>'
-);
-document.write(
-  "<style>#ember-testing-container { position: fixed; background: white; bottom: 0; right: 0; width: 640px; height: 384px; overflow: auto; z-index: 9999; border: 1px solid #ccc; transform: translateZ(0)} #ember-testing { width: 200%; height: 200%; transform: scale(0.5); transform-origin: top left; }</style>"
+document.body.insertAdjacentHTML(
+  "afterbegin",
+  `
+    <div id="ember-testing-container"><div id="ember-testing"></div></div>
+    <style>#ember-testing-container { position: fixed; background: white; bottom: 0; right: 0; width: 640px; height: 384px; overflow: auto; z-index: 9999; border: 1px solid #ccc; transform: translateZ(0)} #ember-testing { width: 200%; height: 200%; transform: scale(0.5); transform-origin: top left; }</style>
+  `
 );
 
 let setupTestsLegacy = require("discourse/tests/setup-tests").setupTestsLegacy;
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 5773efd851f..f069f5560c1 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -153,7 +153,7 @@ module ApplicationHelper
   def preload_script_url(url)
     <<~HTML.html_safe
       <link rel="preload" href="#{url}" as="script">
-      <script src="#{url}"></script>
+      <script defer src="#{url}"></script>
     HTML
   end
 
diff --git a/app/models/theme.rb b/app/models/theme.rb
index 5c510086f7f..6488b36e52d 100644
--- a/app/models/theme.rb
+++ b/app/models/theme.rb
@@ -154,7 +154,7 @@ class Theme < ActiveRecord::Base
     SvgSprite.expire_cache
   end
 
-  BASE_COMPILER_VERSION = 55
+  BASE_COMPILER_VERSION = 56
   def self.compiler_version
     get_set_cache "compiler_version" do
       dependencies = [
@@ -391,7 +391,7 @@ class Theme < ActiveRecord::Base
       end
       caches = JavascriptCache.where(theme_id: theme_ids)
       caches = caches.sort_by { |cache| theme_ids.index(cache.theme_id) }
-      return caches.map { |c| "<script src='#{c.url}' data-theme-id='#{c.theme_id}'></script>" }.join("\n")
+      return caches.map { |c| "<script defer src='#{c.url}' data-theme-id='#{c.theme_id}'></script>" }.join("\n")
     end
     list_baked_fields(theme_ids, target, name).map { |f| f.value_baked || f.value }.join("\n")
   end
diff --git a/app/models/theme_field.rb b/app/models/theme_field.rb
index bdc017c6617..a48b5f92186 100644
--- a/app/models/theme_field.rb
+++ b/app/models/theme_field.rb
@@ -149,7 +149,7 @@ class ThemeField < ActiveRecord::Base
     javascript_cache.content = js_compiler.content
     javascript_cache.save!
 
-    doc.add_child("<script src='#{javascript_cache.url}' data-theme-id='#{theme_id}'></script>") if javascript_cache.content.present?
+    doc.add_child("<script defer src='#{javascript_cache.url}' data-theme-id='#{theme_id}'></script>") if javascript_cache.content.present?
     [doc.to_s, errors&.join("\n")]
   end
 
@@ -265,7 +265,7 @@ class ThemeField < ActiveRecord::Base
     javascript_cache.content = js_compiler.content
     javascript_cache.save!
     doc = ""
-    doc = "<script src='#{javascript_cache.url}' data-theme-id='#{theme_id}'></script>" if javascript_cache.content.present?
+    doc = "<script defer src='#{javascript_cache.url}' data-theme-id='#{theme_id}'></script>" if javascript_cache.content.present?
     [doc, errors&.join("\n")]
   end
 
diff --git a/app/views/layouts/application.html.erb b/app/views/layouts/application.html.erb
index 83e56dff16e..0ab67a126c0 100644
--- a/app/views/layouts/application.html.erb
+++ b/app/views/layouts/application.html.erb
@@ -112,11 +112,11 @@
 
     <div class="hidden" id="data-preloaded" data-preloaded="<%= preloaded_json %>"></div>
 
-    <script src="<%= script_asset_path "start-discourse" %>"></script>
+    <script defer src="<%= script_asset_path "start-discourse" %>"></script>
 
     <%= yield :data %>
 
-    <script src="<%= script_asset_path "browser-update" %>"></script>
+    <script defer src="<%= script_asset_path "browser-update" %>"></script>
 
     <%- unless customization_disabled? %>
       <%= theme_lookup("body_tag") %>
diff --git a/spec/helpers/application_helper_spec.rb b/spec/helpers/application_helper_spec.rb
index e7af0c68118..fdf4ce1faa2 100644
--- a/spec/helpers/application_helper_spec.rb
+++ b/spec/helpers/application_helper_spec.rb
@@ -7,7 +7,7 @@ describe ApplicationHelper do
     def preload_link(url)
       <<~HTML
           <link rel="preload" href="#{url}" as="script">
-          <script src="#{url}"></script>
+          <script defer src="#{url}"></script>
       HTML
     end
 
diff --git a/spec/models/theme_field_spec.rb b/spec/models/theme_field_spec.rb
index ad43c0d1e09..c4eca24304e 100644
--- a/spec/models/theme_field_spec.rb
+++ b/spec/models/theme_field_spec.rb
@@ -75,7 +75,7 @@ describe ThemeField do
 
     theme_field = ThemeField.create!(theme_id: 1, target_id: 0, name: "header", value: html)
     theme_field.ensure_baked!
-    expect(theme_field.value_baked).to include("<script src=\"#{theme_field.javascript_cache.url}\" data-theme-id=\"1\"></script>")
+    expect(theme_field.value_baked).to include("<script defer=\"\" src=\"#{theme_field.javascript_cache.url}\" data-theme-id=\"1\"></script>")
     expect(theme_field.value_baked).to include("external-script.js")
     expect(theme_field.value_baked).to include('<script type="text/template"')
     expect(theme_field.javascript_cache.content).to include('a = "inline discourse plugin"')
@@ -110,7 +110,7 @@ HTML
     field = ThemeField.create!(theme_id: 1, target_id: 0, name: "header", value: html)
     field.ensure_baked!
     expect(field.error).not_to eq(nil)
-    expect(field.value_baked).to include("<script src=\"#{field.javascript_cache.url}\" data-theme-id=\"1\"></script>")
+    expect(field.value_baked).to include("<script defer=\"\" src=\"#{field.javascript_cache.url}\" data-theme-id=\"1\"></script>")
     expect(field.javascript_cache.content).to include("Theme Transpilation Error:")
 
     field.update!(value: '')
@@ -130,7 +130,7 @@ HTML
     theme_field.ensure_baked!
     javascript_cache = theme_field.javascript_cache
 
-    expect(theme_field.value_baked).to include("<script src=\"#{javascript_cache.url}\" data-theme-id=\"1\"></script>")
+    expect(theme_field.value_baked).to include("<script defer=\"\" src=\"#{javascript_cache.url}\" data-theme-id=\"1\"></script>")
     expect(javascript_cache.content).to include("testing-div")
     expect(javascript_cache.content).to include("string_setting")
     expect(javascript_cache.content).to include("test text \\\" 123!")
@@ -378,7 +378,7 @@ HTML
     describe "javascript cache" do
       it "is generated correctly" do
         fr1.ensure_baked!
-        expect(fr1.value_baked).to include("<script src='#{fr1.javascript_cache.url}' data-theme-id='#{fr1.theme_id}'></script>")
+        expect(fr1.value_baked).to include("<script defer src='#{fr1.javascript_cache.url}' data-theme-id='#{fr1.theme_id}'></script>")
         expect(fr1.javascript_cache.content).to include("bonjourworld")
         expect(fr1.javascript_cache.content).to include("helloworld")
         expect(fr1.javascript_cache.content).to include("enval1")