diff --git a/demo/src/html/index.html.template b/demo/src/html/index.html.template
index 021a9dc55f..368dcc08e3 100644
--- a/demo/src/html/index.html.template
+++ b/demo/src/html/index.html.template
@@ -84,9 +84,6 @@
     <%= renderTemplate("../../../src/html/_js_base.html.template") %>
     <%= renderTemplate("../../../src/html/_preload_roboto.html.template") %>
     <script>
-      if (!window.globalThis) {
-        window.globalThis = window;
-      }
       // Safari 12 and below does not have a compliant ES2015 implementation of template literals, so we ship ES5
       if (!isS11_12) {
         <% for (const entry of latestEntryJS) { %>
diff --git a/src/components/ha-icon.ts b/src/components/ha-icon.ts
index a93be2c798..0ce63ed8ba 100644
--- a/src/components/ha-icon.ts
+++ b/src/components/ha-icon.ts
@@ -88,8 +88,8 @@ export class HaIcon extends LitElement {
     }
 
     if (!MDI_PREFIXES.includes(iconPrefix)) {
-      if (iconPrefix in customIcons) {
-        const customIcon = customIcons[iconPrefix];
+      const customIcon = customIcons[iconPrefix];
+      if (customIcon) {
         if (customIcon && typeof customIcon.getIcon === "function") {
           this._setCustomPath(customIcon.getIcon(iconName), requestedIcon);
         }
diff --git a/src/data/custom_icons.ts b/src/data/custom_icons.ts
index 1fad2b9a66..8728116a0e 100644
--- a/src/data/custom_icons.ts
+++ b/src/data/custom_icons.ts
@@ -36,5 +36,4 @@ export const customIcons = new Proxy(customIconsWindow.customIcons!, {
           getIcon: customIconsets[prop],
         }
       : undefined),
-  has: (obj, prop: string) => prop in obj || prop in customIconsets,
 });
diff --git a/src/entrypoints/core.ts b/src/entrypoints/core.ts
index 2e34faae09..74cfd72a5f 100644
--- a/src/entrypoints/core.ts
+++ b/src/entrypoints/core.ts
@@ -94,7 +94,7 @@ const connProm = async (auth) => {
   }
 };
 
-if (__DEV__) {
+if (__DEV__ && "performance" in window) {
   // Remove adoptedStyleSheets so style inspector works on shadow DOM.
   // @ts-ignore
   delete Document.prototype.adoptedStyleSheets;
diff --git a/src/html/authorize.html.template b/src/html/authorize.html.template
index 5f9c58f244..96107af171 100644
--- a/src/html/authorize.html.template
+++ b/src/html/authorize.html.template
@@ -41,9 +41,6 @@
     <%= renderTemplate("_js_base.html.template") %>
     <%= renderTemplate("_preload_roboto.html.template") %>
     <script crossorigin="use-credentials">
-      if (!window.globalThis) {
-        window.globalThis = window;
-      }
       // Safari 12 and below does not have a compliant ES2015 implementation of template literals, so we ship ES5
       if (!isS11_12) {
         <% for (const entry of latestEntryJS) { %>
diff --git a/src/html/index.html.template b/src/html/index.html.template
index c8aae499b6..977da8f617 100644
--- a/src/html/index.html.template
+++ b/src/html/index.html.template
@@ -84,9 +84,6 @@
     <%= renderTemplate("_js_base.html.template") %>
     <%= renderTemplate("_preload_roboto.html.template") %>
     <script <% if (!useWDS) { %>crossorigin="use-credentials"<% } %>>
-      if (!window.globalThis) {
-        window.globalThis = window;
-      }
       // Safari 12 and below does not have a compliant ES2015 implementation of template literals, so we ship ES5
       if (!isS11_12) {
         <% for (const entry of latestEntryJS) { %>
diff --git a/src/html/onboarding.html.template b/src/html/onboarding.html.template
index 7e6f828972..7e34e0bc7a 100644
--- a/src/html/onboarding.html.template
+++ b/src/html/onboarding.html.template
@@ -71,9 +71,6 @@
     <%= renderTemplate("_js_base.html.template") %>
     <%= renderTemplate("_preload_roboto.html.template") %>
     <script crossorigin="use-credentials">
-      if (!window.globalThis) {
-        window.globalThis = window;
-      }
       // Safari 12 and below does not have a compliant ES2015 implementation of template literals, so we ship ES5
       if (!isS11_12) {
         <% for (const entry of latestEntryJS) { %>
diff --git a/src/resources/compatibility.ts b/src/resources/compatibility.ts
index e9c678c9fc..eca81afe09 100644
--- a/src/resources/compatibility.ts
+++ b/src/resources/compatibility.ts
@@ -66,3 +66,27 @@ if (Element.prototype.getAttributeNames === undefined) {
     return result;
   };
 }
+
+// Source: https://gist.github.com/rebelchris/365f26f95d7e9f432f64f21886d9b9ef
+if (!Element.prototype.toggleAttribute) {
+  Element.prototype.toggleAttribute = function (name, force) {
+    if (force !== undefined) {
+      force = !!force;
+    }
+
+    if (this.hasAttribute(name)) {
+      if (force) {
+        return true;
+      }
+
+      this.removeAttribute(name);
+      return false;
+    }
+    if (force === false) {
+      return false;
+    }
+
+    this.setAttribute(name, "");
+    return true;
+  };
+}