diff --git a/build-scripts/bundle.cjs b/build-scripts/bundle.cjs
index 3a3c6929b8..ef59a29631 100644
--- a/build-scripts/bundle.cjs
+++ b/build-scripts/bundle.cjs
@@ -55,7 +55,7 @@ module.exports.definedVars = ({ isProdBuild, latestBuild, defineOverlay }) => ({
   __STATIC_PATH__: "/static/",
   __HASS_URL__: `\`${
     "HASS_URL" in process.env
-      ? process.env["HASS_URL"]
+      ? process.env.HASS_URL
       : "${location.protocol}//${location.host}"
   }\``,
   "process.env.NODE_ENV": JSON.stringify(
diff --git a/build-scripts/gulp/entry-html.js b/build-scripts/gulp/entry-html.js
index 016aab28c2..b5994b4d68 100644
--- a/build-scripts/gulp/entry-html.js
+++ b/build-scripts/gulp/entry-html.js
@@ -56,6 +56,7 @@ const getCommonTemplateVars = () => {
   );
   return {
     modernRegex: compileRegex(browserRegexes.concat(haMacOSRegex)).toString(),
+    hassUrl: process.env.HASS_URL || "",
   };
 };
 
diff --git a/src/components/ha-hls-player.ts b/src/components/ha-hls-player.ts
index c9ac9e1571..64ba51706e 100644
--- a/src/components/ha-hls-player.ts
+++ b/src/components/ha-hls-player.ts
@@ -123,7 +123,7 @@ class HaHLSPlayer extends LitElement {
     try {
       const { url } = await fetchStreamUrl(this.hass!, this.entityid);
 
-      this._url = url;
+      this._url = this.hass.hassUrl(url);
       this._cleanUp();
       this._resetError();
       this._startHls();
@@ -181,15 +181,7 @@ class HaHLSPlayer extends LitElement {
     let playlist_url: string;
     if (match !== null && matchTwice === null) {
       // Only send the regular playlist url if we match exactly once
-      // In case we arrive here with a relative URL, we need to provide a valid
-      // base/absolute URL to avoid the URL() constructor throwing an error.
-      let base_url: string;
-      try {
-        base_url = new URL(this._url).href;
-      } catch (_error) {
-        base_url = new URL(this._url, window.location.href).href;
-      }
-      playlist_url = new URL(match[3], base_url).href;
+      playlist_url = new URL(match[3], this._url).href;
     } else {
       playlist_url = this._url;
     }
@@ -219,7 +211,7 @@ class HaHLSPlayer extends LitElement {
     await this.hass!.auth.external!.fireMessage({
       type: "exoplayer/play_hls",
       payload: {
-        url: new URL(url, window.location.href).toString(),
+        url,
         muted: this.muted,
       },
     });
diff --git a/src/components/ha-picture-upload.ts b/src/components/ha-picture-upload.ts
index 414236e262..ade3d9fa0f 100644
--- a/src/components/ha-picture-upload.ts
+++ b/src/components/ha-picture-upload.ts
@@ -198,7 +198,7 @@ export class HaPictureUpload extends LitElement {
             const url = generateImageThumbnailUrl(mediaId, undefined, true);
             let data;
             try {
-              data = await getImageData(url);
+              data = await getImageData(this.hass, url);
             } catch (err: any) {
               showAlertDialog(this, {
                 text: err.toString(),
diff --git a/src/components/user/ha-person-badge.ts b/src/components/user/ha-person-badge.ts
index 675166c962..8b5078b2c1 100644
--- a/src/components/user/ha-person-badge.ts
+++ b/src/components/user/ha-person-badge.ts
@@ -4,9 +4,12 @@ import { classMap } from "lit/directives/class-map";
 import { styleMap } from "lit/directives/style-map";
 import type { BasePerson } from "../../data/person";
 import { computeUserInitials } from "../../data/user";
+import type { HomeAssistant } from "../../types";
 
 @customElement("ha-person-badge")
 class PersonBadge extends LitElement {
+  @property({ attribute: false }) public hass!: HomeAssistant;
+
   @property({ attribute: false }) public person?: BasePerson;
 
   protected render() {
@@ -18,7 +21,9 @@ class PersonBadge extends LitElement {
 
     if (picture) {
       return html`<div
-        style=${styleMap({ backgroundImage: `url(${picture})` })}
+        style=${styleMap({
+          backgroundImage: `url(${this.hass.hassUrl(picture)})`,
+        })}
         class="picture"
       ></div>`;
     }
diff --git a/src/components/user/ha-user-badge.ts b/src/components/user/ha-user-badge.ts
index 421f65468b..df1520d60b 100644
--- a/src/components/user/ha-user-badge.ts
+++ b/src/components/user/ha-user-badge.ts
@@ -50,7 +50,9 @@ class UserBadge extends LitElement {
 
     if (picture) {
       return html`<div
-        style=${styleMap({ backgroundImage: `url(${picture})` })}
+        style=${styleMap({
+          backgroundImage: `url(${this.hass.hassUrl(picture)})`,
+        })}
         class="picture"
       ></div>`;
     }
diff --git a/src/data/backup_onboarding.ts b/src/data/backup_onboarding.ts
index bca3253679..80c37126bb 100644
--- a/src/data/backup_onboarding.ts
+++ b/src/data/backup_onboarding.ts
@@ -22,7 +22,7 @@ export interface BackupOnboardingConfig extends BackupOnboardingInfo {
 
 export const fetchBackupOnboardingInfo = async () =>
   handleFetchPromise<BackupOnboardingConfig>(
-    fetch("/api/onboarding/backup/info")
+    fetch(`${__HASS_URL__}/api/onboarding/backup/info`)
   );
 
 export interface RestoreOnboardingBackupParams {
@@ -38,7 +38,7 @@ export const restoreOnboardingBackup = async (
   params: RestoreOnboardingBackupParams
 ) =>
   handleFetchPromise(
-    fetch("/api/onboarding/backup/restore", {
+    fetch(`${__HASS_URL__}/api/onboarding/backup/restore`, {
       method: "POST",
       body: JSON.stringify(params),
     })
@@ -58,7 +58,7 @@ export const uploadOnboardingBackup = async (
   });
 
   return handleFetchPromise(
-    fetch(`/api/onboarding/backup/upload?${params.toString()}`, {
+    fetch(`${__HASS_URL__}/api/onboarding/backup/upload?${params.toString()}`, {
       method: "POST",
       body: fd,
     })
diff --git a/src/data/hassio/backup.ts b/src/data/hassio/backup.ts
index 09a410fe6b..66684d1698 100644
--- a/src/data/hassio/backup.ts
+++ b/src/data/hassio/backup.ts
@@ -214,7 +214,7 @@ export const uploadBackup = async (
     );
   } else {
     // When called from onboarding we don't have hass
-    resp = await fetch("/api/hassio/backups/new/upload", {
+    resp = await fetch(`${__HASS_URL__}/api/hassio/backups/new/upload`, {
       method: "POST",
       body: fd,
     });
diff --git a/src/data/image_upload.ts b/src/data/image_upload.ts
index 225c473f37..c1744db3f2 100644
--- a/src/data/image_upload.ts
+++ b/src/data/image_upload.ts
@@ -81,8 +81,8 @@ export const deleteImage = (hass: HomeAssistant, id: string) =>
     image_id: id,
   });
 
-export const getImageData = async (url: string) => {
-  const response = await fetch(url);
+export const getImageData = async (hass: HomeAssistant, url: string) => {
+  const response = await fetch(hass.hassUrl(url));
 
   if (!response.ok) {
     throw new Error(
diff --git a/src/data/onboarding.ts b/src/data/onboarding.ts
index cfdf7fd21e..b69e12faad 100644
--- a/src/data/onboarding.ts
+++ b/src/data/onboarding.ts
@@ -37,7 +37,7 @@ export interface OnboardingStep {
 }
 
 export const fetchOnboardingOverview = () =>
-  fetch("/api/onboarding", { credentials: "same-origin" });
+  fetch(`${__HASS_URL__}/api/onboarding`, { credentials: "same-origin" });
 
 export const onboardUserStep = (params: {
   client_id: string;
@@ -47,7 +47,7 @@ export const onboardUserStep = (params: {
   language: string;
 }) =>
   handleFetchPromise<OnboardingUserStepResponse>(
-    fetch("/api/onboarding/users", {
+    fetch(`${__HASS_URL__}/api/onboarding/users`, {
       method: "POST",
       credentials: "same-origin",
       body: JSON.stringify(params),
@@ -74,9 +74,12 @@ export const onboardIntegrationStep = (
   );
 
 export const fetchInstallationType = async (): Promise<InstallationType> => {
-  const response = await fetch("/api/onboarding/installation_type", {
-    method: "GET",
-  });
+  const response = await fetch(
+    `${__HASS_URL__}/api/onboarding/installation_type`,
+    {
+      method: "GET",
+    }
+  );
 
   if (response.status === 401) {
     throw Error("unauthorized");
diff --git a/src/html/_header.html.template b/src/html/_header.html.template
index 0a3c1360dd..772bf10050 100644
--- a/src/html/_header.html.template
+++ b/src/html/_header.html.template
@@ -1,5 +1,5 @@
 <meta charset="utf-8" />
-<link rel="manifest" href="/manifest.json" crossorigin="use-credentials" />
+<link rel="manifest" href="<%= hassUrl %>/manifest.json" crossorigin="use-credentials" />
 <link rel="icon" href="/static/icons/favicon.ico" />
 <% for (const entry of latestEntryJS) { %>
   <link rel="modulepreload" href="<%= entry %>" crossorigin="use-credentials" />
diff --git a/src/html/authorize.html.template b/src/html/authorize.html.template
index 9bf63eaa94..657e23e548 100644
--- a/src/html/authorize.html.template
+++ b/src/html/authorize.html.template
@@ -55,7 +55,7 @@
     <%= renderTemplate("_script_loader.html.template") %>
     <script crossorigin="use-credentials">
       if (window.latestJS) {
-        window.providersPromise = fetch("/auth/providers", {
+        window.providersPromise = fetch("<%= hassUrl %>/auth/providers", {
           credentials: "same-origin",
         });
       }
diff --git a/src/html/index.html.template b/src/html/index.html.template
index 5e43b50409..6c2aac0bdf 100644
--- a/src/html/index.html.template
+++ b/src/html/index.html.template
@@ -89,11 +89,13 @@
         window.latestJS = true;
       }
     </script>
-    <script>
-    {%- for extra_module in extra_modules -%}
-    import("{{ extra_module }}");
-    {%- endfor -%}
-    </script>
+    <% if (obj.hassUrl === "") { %>
+      <script>
+        {%- for extra_module in extra_modules -%}
+        import("{{ extra_module }}");
+        {%- endfor -%}
+      </script>
+    <% } %>
     <script>
         if (!window.latestJS) {
           window.customPanelJS = "<%= es5CustomPanelJS %>";
@@ -102,12 +104,15 @@
           <% } %>
         }
     </script>
-    <script>
-      if (!window.latestJS) {
-        {%- for extra_script in extra_js_es5 -%}
-        _ls("{{ extra_script }}");
-        {%- endfor -%}
-      }
-    </script>
+
+    <% if (obj.hassUrl === "") { %>
+      <script>
+        if (!window.latestJS) {
+          {%- for extra_script in extra_js_es5 -%}
+          _ls("{{ extra_script }}");
+          {%- endfor -%}
+        }
+      </script>
+    <% } %>
   </body>
 </html>
diff --git a/src/html/onboarding.html.template b/src/html/onboarding.html.template
index b19f68628c..20959221e8 100644
--- a/src/html/onboarding.html.template
+++ b/src/html/onboarding.html.template
@@ -51,7 +51,7 @@
     <%= renderTemplate("_script_loader.html.template") %>
     <script crossorigin="use-credentials">
       if (window.latestJS) {
-        window.stepsPromise = fetch("/api/onboarding", {
+        window.stepsPromise = fetch("<%= hassUrl %>/api/onboarding", {
           credentials: "same-origin",
         });
       }
diff --git a/test/data/image_upload.test.ts b/test/data/image_upload.test.ts
index 805cc86b8b..ae97ed261b 100644
--- a/test/data/image_upload.test.ts
+++ b/test/data/image_upload.test.ts
@@ -128,12 +128,15 @@ describe("image_upload", () => {
   });
 
   describe("getImageData", () => {
+    const hass = {
+      hassUrl: vi.fn((url) => url),
+    } as unknown as HomeAssistant;
     it("should fetch image data", async () => {
       global.fetch = vi.fn().mockResolvedValue({
         ok: true,
         blob: vi.fn().mockResolvedValue(new Blob()),
       });
-      const data = await getImageData("http://example.com/image.png");
+      const data = await getImageData(hass, "http://example.com/image.png");
       expect(global.fetch).toHaveBeenCalledWith("http://example.com/image.png");
       expect(data).toBeInstanceOf(Blob);
     });
@@ -143,7 +146,7 @@ describe("image_upload", () => {
         .fn()
         .mockResolvedValue({ ok: false, statusText: "Not Found" });
       await expect(
-        getImageData("http://example.com/image.png")
+        getImageData(hass, "http://example.com/image.png")
       ).rejects.toThrow("Failed to fetch image: Not Found");
     });
   });