Oops we should register a service worker as long as it is supported.

app/views/common/_discourse_javascript.html.erb

@@ -44,9 +44,7 @@
     Discourse.SiteSettings = ps.get('siteSettings');
     Discourse.LetterAvatarVersion = '<%= LetterAvatar.version %>';
     Discourse.MarkdownItURL = '<%= asset_url('markdown-it-bundle.js') %>';
-    <%- if DiscoursePluginRegistry.service_workers.present? %>
     Discourse.ServiceWorkerURL = '<%= Rails.application.assets_manifest.assets['service-worker.js'] %>'
-    <%- end %>
     I18n.defaultLocale = '<%= SiteSetting.default_locale %>';
     Discourse.start();
     Discourse.set('assetVersion','<%= Discourse.assets_digest %>');