diff --git a/src/backend/controllers/auth/AuthController.test.ts b/src/backend/controllers/auth/AuthController.test.ts
index a58a72b1b..97790ec4c 100644
--- a/src/backend/controllers/auth/AuthController.test.ts
+++ b/src/backend/controllers/auth/AuthController.test.ts
@@ -3119,6 +3119,27 @@ describe('AuthController.handleGetUserAppToken + handleCheckApp', () => {
         expect(bootstrapped).toBeTruthy();
         expect(bootstrapped?.owner_user_id).toBe(owner!.id);
     });
+
+    it('supports browser extension origins in handleGetUserAppToken', async () => {
+        // Random id: a pre-existing row for this origin would resolve through
+        // the canonical lookup and never exercise the bootstrap path.
+        const origin = `chrome-extension://${uuidv4()}`;
+        const res = makeRes();
+        await inCtx(actor, () =>
+            controller.handleGetUserAppToken(
+                makeReq({ origin }, { actor }),
+                res,
+            ),
+        );
+        const body = res.body as { token: string; app_uid: string };
+        expect(body.app_uid).toBe(
+            `app-${uuidv5(origin, APP_ORIGIN_UUID_NAMESPACE)}`,
+        );
+        const bootstrapped = await server.stores.app.getByUid(body.app_uid);
+        expect(bootstrapped?.index_url).toBe(origin);
+        // Proves the row came from the bootstrap path, not an earlier test.
+        expect(bootstrapped?.description).toMatch(/^App created from origin /);
+    });
 });
 
 // ── Access tokens: create + revoke ─────────────────────────────────
diff --git a/src/backend/drivers/apps/AppDriver.js b/src/backend/drivers/apps/AppDriver.js
index f2d88470e..1e4134487 100644
--- a/src/backend/drivers/apps/AppDriver.js
+++ b/src/backend/drivers/apps/AppDriver.js
@@ -48,6 +48,7 @@ import {
     validateJsonObject,
     validateString,
     validateUrl,
+    WEB_AND_EXTENSION_PROTOCOLS,
 } from '../../util/validation.js';
 import { PuterDriver } from '../types.js';
 
@@ -632,6 +633,7 @@ export class AppDriver extends PuterDriver {
                 key: 'index_url',
                 maxLen: 3000,
                 required: isCreate,
+                protocols: WEB_AND_EXTENSION_PROTOCOLS,
             });
             // Only enforce on new/changed values so rows that already
             // carry a reserved host (migration-seeded builtins) can still
diff --git a/src/backend/services/auth/AuthService.test.ts b/src/backend/services/auth/AuthService.test.ts
index aede3e864..9f67606c4 100644
--- a/src/backend/services/auth/AuthService.test.ts
+++ b/src/backend/services/auth/AuthService.test.ts
@@ -18,7 +18,7 @@
  */
 
 import jwt from 'jsonwebtoken';
-import { v4 as uuidv4 } from 'uuid';
+import { v4 as uuidv4, v5 as uuidv5 } from 'uuid';
 import { afterAll, beforeAll, describe, expect, it } from 'vitest';
 import { makeActor, type Actor } from '../../core/actor.js';
 import { PuterServer } from '../../server.js';
@@ -1631,14 +1631,81 @@ describe('AuthService (integration)', () => {
             'data:text/html,<script>alert(1)</script>',
             'file:///etc/passwd',
             'vbscript:msgbox(1)',
-        ])('throws 400 for non-http(s) scheme %s', async (origin) => {
-            // These parse fine via `new URL()` but must never become a
-            // bootstrap app `index_url` — that would be a stored XSS /
-            // code-execution vector when launched as `iframe.src`.
-            await expect(
-                authService.appUidFromOrigin(origin),
-            ).rejects.toMatchObject({ statusCode: 400 });
+        ])(
+            'throws 400 for unsafe non-web/non-extension scheme %s',
+            async (origin) => {
+                // These parse fine via `new URL()` but must never become a
+                // bootstrap app `index_url` — that would be a stored XSS /
+                // code-execution vector when launched as `iframe.src`.
+                await expect(
+                    authService.appUidFromOrigin(origin),
+                ).rejects.toMatchObject({ statusCode: 400 });
+            },
+        );
+
+        // Mirrors APP_ORIGIN_UUID_NAMESPACE in AuthService: changing it
+        // changes every origin-derived app uid in the fleet.
+        const APP_ORIGIN_UUID_NAMESPACE =
+            '33de3768-8ee0-43e9-9e73-db192b97a5d8';
+        // Unique per run — a real `apps` row carrying the same origin as its
+        // `index_url` resolves ahead of the uuidv5 fallback.
+        const extensionId = uuidv4();
+
+        it.each([
+            `chrome-extension://${extensionId}`,
+            `moz-extension://${extensionId}`,
+            `safari-extension://${extensionId}`,
+            `safari-web-extension://${extensionId}`,
+        ])('derives the app uid for extension origin %s', async (origin) => {
+            const uid = await authService.appUidFromOrigin(origin);
+            expect(uid).toBe(
+                `app-${uuidv5(origin, APP_ORIGIN_UUID_NAMESPACE)}`,
+            );
+            expect(await authService.appUidFromOrigin(origin)).toBe(uid);
         });
+
+        it('gives two extensions two different app uids', async () => {
+            const a = await authService.appUidFromOrigin(
+                `chrome-extension://${uuidv4()}`,
+            );
+            const b = await authService.appUidFromOrigin(
+                `chrome-extension://${uuidv4()}`,
+            );
+            expect(a).not.toBe(b);
+        });
+
+        it('resolves an extension id case-insensitively', async () => {
+            // `new URL()` lowercases http(s) hosts but leaves opaque ones
+            // alone, so without normalization one extension would get two
+            // uids, two AppData trees and two permission sets.
+            const id = uuidv4();
+            expect(
+                await authService.appUidFromOrigin(
+                    `chrome-extension://${id.toUpperCase()}`,
+                ),
+            ).toBe(
+                await authService.appUidFromOrigin(`chrome-extension://${id}`),
+            );
+        });
+
+        it.each([
+            // Extension schemes are not "special", so `new URL()` accepts them
+            // with no authority — which would slip past every host-based guard.
+            'chrome-extension:',
+            'moz-extension:',
+            // Near-misses: no browser emits any of these.
+            'extension://my-extension-id',
+            'web-extension://my-extension-id',
+            'ms-browser-extension://my-extension-id',
+            'chrome-extensions://my-extension-id',
+        ])(
+            'throws 400 for host-less or non-browser scheme %s',
+            async (origin) => {
+                await expect(
+                    authService.appUidFromOrigin(origin),
+                ).rejects.toMatchObject({ statusCode: 400 });
+            },
+        );
     });
 
     describe('subdomainOwnerIdFromOrigin', () => {
diff --git a/src/backend/services/auth/AuthService.ts b/src/backend/services/auth/AuthService.ts
index e4a7aecab..f0df2a8a7 100644
--- a/src/backend/services/auth/AuthService.ts
+++ b/src/backend/services/auth/AuthService.ts
@@ -26,6 +26,7 @@ import {
     type Actor,
 } from '../../core/actor';
 import { HttpError } from '../../core/http/HttpError.js';
+import { WEB_AND_EXTENSION_PROTOCOLS } from '../../util/validation.js';
 import {
     ASSET_WINDOW_SECONDS,
     WEB_WINDOW_SECONDS,
@@ -915,10 +916,13 @@ export class AuthService extends PuterService {
         return this.#normalizedOrigin(parsed);
     }
 
-    /** Scheme + host + explicit port, with no trailing separator. */
+    /** Scheme + lowercased host + explicit port, with no trailing separator. */
     #normalizedOrigin(parsed: URL): string {
         const port = parsed.port ? `:${parsed.port}` : '';
-        return `${parsed.protocol}//${parsed.hostname}${port}`;
+        // `new URL()` lowercases http(s) hosts but leaves opaque ones alone, so
+        // without this an extension id in two spellings hashes to two app uids
+        // (and misses the blocklist, which matches on a lowercased host).
+        return `${parsed.protocol}//${parsed.hostname.toLowerCase()}${port}`;
     }
 
     /**
@@ -1786,14 +1790,15 @@ export class AuthService extends PuterService {
     #originFromUrl(url: string): string | null {
         try {
             const parsed = new URL(url);
-            // A real web origin is always http(s). `new URL()` happily parses
-            // `javascript:`, `data:`, `file:`, `vbscript:`, etc.; if one of
-            // those slips through it ends up persisted as an app `index_url`
-            // (see AppStore.createFromOrigin) and later loaded as `iframe.src`
-            // — an XSS/code-execution primitive. Reject anything that isn't
-            // http(s) so the bootstrap path matches AppDriver's validateUrl
-            // allow-list.
-            if (parsed.protocol !== 'http:' && parsed.protocol !== 'https:') {
+            // This gets persisted as an app `index_url` and later loaded as
+            // `iframe.src` (see AppStore.createFromOrigin), so anything outside
+            // the allow-list is a stored code-execution vector.
+            if (!WEB_AND_EXTENSION_PROTOCOLS.includes(parsed.protocol)) {
+                return null;
+            }
+            // Extension schemes aren't "special", so `new URL()` accepts them
+            // with no authority at all (`chrome-extension:`).
+            if (!parsed.hostname) {
                 return null;
             }
             return this.#normalizedOrigin(parsed);
diff --git a/src/backend/stores/app/AppStore.js b/src/backend/stores/app/AppStore.js
index ada84646d..46ed2da5d 100644
--- a/src/backend/stores/app/AppStore.js
+++ b/src/backend/stores/app/AppStore.js
@@ -21,7 +21,10 @@ import { v4 as uuidv4 } from 'uuid';
 import { PuterStore } from '../types';
 import { HttpError } from '../../core/http/HttpError.js';
 import { isUniqueViolation } from '../../util/dbError.js';
-import { validateUrl } from '../../util/validation.js';
+import {
+    validateUrl,
+    WEB_AND_EXTENSION_PROTOCOLS,
+} from '../../util/validation.js';
 
 /**
  * Persistence + cache for the `apps` table.
@@ -470,11 +473,14 @@ export class AppStore extends PuterStore {
         { ownerUserId = null } = {},
     ) {
         // Bootstrap apps persist `origin` straight into `index_url`, which is
-        // later loaded as `iframe.src`. Enforce the same http(s) scheme
-        // allow-list as the AppDriver create/update path so a caller-supplied
+        // later loaded as `iframe.src`. Enforce the same scheme allow-list
+        // as the AppDriver create/update path so a caller-supplied
         // `javascript:`/`data:`/`file:` origin can never become a stored,
         // launchable code-execution vector.
-        validateUrl(origin, { key: 'origin' });
+        validateUrl(origin, {
+            key: 'origin',
+            protocols: WEB_AND_EXTENSION_PROTOCOLS,
+        });
 
         const fields = {
             name: uid,
diff --git a/src/backend/stores/app/AppStore.test.js b/src/backend/stores/app/AppStore.test.js
index 4019f5043..40c0a7199 100644
--- a/src/backend/stores/app/AppStore.test.js
+++ b/src/backend/stores/app/AppStore.test.js
@@ -776,6 +776,10 @@ describe('AppStore CRUD and cache invalidation', () => {
         'javascript:alert(1)',
         'data:text/html,<script>alert(1)</script>',
         'file:///etc/passwd',
+        // Allow-listed scheme, but `new URL()` accepts it with no authority.
+        'chrome-extension:',
+        // Not a scheme any browser emits.
+        'extension://my-extension-id',
     ])('refuses to bootstrap an app from the %s origin', async (origin) => {
         await expect(
             appStore.createFromOrigin(
@@ -785,6 +789,16 @@ describe('AppStore CRUD and cache invalidation', () => {
         ).rejects.toMatchObject({ statusCode: 400 });
     });
 
+    it('creates an origin-bootstrap app for a browser extension origin', async () => {
+        const uid = `app-ext-${Math.random().toString(36).slice(2, 10)}`;
+        const origin = `chrome-extension://${uid}`;
+
+        const app = await appStore.createFromOrigin(uid, origin);
+
+        expect(app.uid).toBe(uid);
+        expect(app.index_url).toBe(origin);
+    });
+
     it('returns the existing row when the deterministic uid was already inserted', async () => {
         const uid = `app-origin-${Math.random().toString(36).slice(2, 10)}`;
         const origin = `https://${uid}.example.com`;
diff --git a/src/backend/util/validation.js b/src/backend/util/validation.js
index 359043bcf..a98da504e 100644
--- a/src/backend/util/validation.js
+++ b/src/backend/util/validation.js
@@ -24,6 +24,31 @@ import { HttpError } from '../core/http/HttpError.js';
  * ...) on failure. Returns the value on success.
  */
 
+/**
+ * Real web origins. Anything outside this list is an XSS/SSRF primitive once
+ * the value is consumed as `iframe.src`, `window.location`, a server-side
+ * fetch, etc. — `new URL()` alone happily parses `javascript:alert(1)`,
+ * `data:text/html,…`, `file:///etc/passwd`, and `vbscript:`.
+ */
+export const WEB_PROTOCOLS = Object.freeze(['http:', 'https:']);
+
+/**
+ * Web origins plus the browser-extension schemes, for app origins and
+ * `index_url` values. Shared by AuthService.#originFromUrl,
+ * AppStore.createFromOrigin and AppDriver.#validateInput.
+ *
+ * Only Chrome derives the extension host from the signing key. Firefox and
+ * Safari generate it per install, so one extension is a distinct origin — and
+ * therefore a distinct app row — for each user who installs it.
+ */
+export const WEB_AND_EXTENSION_PROTOCOLS = Object.freeze([
+    ...WEB_PROTOCOLS,
+    'chrome-extension:',
+    'moz-extension:',
+    'safari-extension:',
+    'safari-web-extension:',
+]);
+
 export function validateString(
     value,
     { key, maxLen, regex, required = true, allowEmpty = false } = {},
@@ -66,13 +91,9 @@ export function validateUrl(
         key,
         maxLen = 3000,
         required = true,
-        // Default allowlist is http(s) only — anything else is an XSS/SSRF
-        // primitive when the value is later consumed as `iframe.src`,
-        // `window.location`, a server-side fetch, etc. `new URL()` alone
-        // happily parses `javascript:alert(1)`, `data:text/html,…`,
-        // `file:///etc/passwd`, and `vbscript:`; callers that need
-        // something exotic must opt in explicitly.
-        protocols = ['http:', 'https:'],
+        // http(s) by default (see WEB_PROTOCOLS); callers that need something
+        // exotic must opt in explicitly.
+        protocols = WEB_PROTOCOLS,
     } = {},
 ) {
     if (value === undefined || value === null) {
@@ -98,6 +119,14 @@ export function validateUrl(
             { legacyCode: 'bad_request' },
         );
     }
+    // Only "special" schemes (http:, https:, ws:, …) require an authority.
+    // `new URL()` accepts `chrome-extension:` and `extension:javascript:alert(1)`
+    // with an empty host, which slips past every host-based guard downstream.
+    if (!parsed.hostname) {
+        throw new HttpError(400, `\`${key}\` must include a host`, {
+            legacyCode: 'bad_request',
+        });
+    }
     return value;
 }
 
diff --git a/src/backend/util/validation.test.js b/src/backend/util/validation.test.js
index f4f23b340..dc9398d55 100644
--- a/src/backend/util/validation.test.js
+++ b/src/backend/util/validation.test.js
@@ -24,6 +24,7 @@ import {
     validateJsonObject,
     validateString,
     validateUrl,
+    WEB_AND_EXTENSION_PROTOCOLS,
 } from './validation.js';
 
 /**
@@ -163,6 +164,56 @@ describe('validateUrl', () => {
         );
     });
 
+    it.each([
+        'chrome-extension://cafneielldmiliebnkhaeaaibinihgpb',
+        'moz-extension://f4b30177-3e5e-49b4-bb50-32df6ff09033',
+        'safari-extension://f4b30177-3e5e-49b4-bb50-32df6ff09033',
+        'safari-web-extension://f4b30177-3e5e-49b4-bb50-32df6ff09033',
+    ])('accepts the browser extension origin %s when opted in', (value) => {
+        expect(
+            validateUrl(value, {
+                key: 'index_url',
+                protocols: WEB_AND_EXTENSION_PROTOCOLS,
+            }),
+        ).toBe(value);
+    });
+
+    it.each([
+        'chrome-extension:',
+        'moz-extension:',
+        'extension:javascript:alert(1)',
+    ])('rejects the host-less value %s', (value) => {
+        // Only "special" schemes require an authority, so these parse with an
+        // empty host and would slip past every host-based guard downstream.
+        expectBadRequest(
+            () =>
+                validateUrl(value, {
+                    key: 'index_url',
+                    protocols: [...WEB_AND_EXTENSION_PROTOCOLS, 'extension:'],
+                }),
+            '`index_url` must include a host',
+        );
+    });
+
+    it.each([
+        'extension://my-extension-id',
+        'web-extension://my-extension-id',
+        'ms-browser-extension://my-extension-id',
+    ])('keeps rejecting the non-browser scheme %s', (value) => {
+        expectBadRequest(
+            () =>
+                validateUrl(value, {
+                    key: 'index_url',
+                    protocols: WEB_AND_EXTENSION_PROTOCOLS,
+                }),
+            'must use one of the following protocols',
+        );
+    });
+
+    it('exposes the extension allow-list as a frozen value', () => {
+        expect(Object.isFrozen(WEB_AND_EXTENSION_PROTOCOLS)).toBe(true);
+    });
+
     it('rejects a missing value when required, passes it through otherwise', () => {
         expectBadRequest(
             () => validateUrl(undefined, { key: 'url' }),