diff --git a/apps/desktop/src/main/capture/auth.ts b/apps/desktop/src/main/capture/auth.ts
index fa51e4349..51311c0db 100644
--- a/apps/desktop/src/main/capture/auth.ts
+++ b/apps/desktop/src/main/capture/auth.ts
@@ -8,6 +8,14 @@ export interface CaptureAuthHeaders {
 
 type Result = { ok: true } | { ok: false; reason: string }
 
+// Capture pairing accepts browser-extension origins only — Chromium (chrome-extension://)
+// and Firefox (moz-extension://). Single source of truth so the two pairing guards can't drift.
+const EXTENSION_ORIGIN_PREFIXES = ['chrome-extension://', 'moz-extension://']
+
+export function isExtensionOrigin(origin: string | undefined): boolean {
+  return !!origin && EXTENSION_ORIGIN_PREFIXES.some((p) => origin.startsWith(p))
+}
+
 function tokenEquals(a: string, b: string): boolean {
   const ab = Buffer.from(a)
   const bb = Buffer.from(b)
diff --git a/apps/desktop/src/main/capture/pairing.test.ts b/apps/desktop/src/main/capture/pairing.test.ts
index 3293fa9e0..2dd73759e 100644
--- a/apps/desktop/src/main/capture/pairing.test.ts
+++ b/apps/desktop/src/main/capture/pairing.test.ts
@@ -41,6 +41,14 @@ describe('pairing', () => {
     expect(isOriginAllowed('https://evil.com')).toBe(false)
   })
 
+  it('claims pairing for a Firefox moz-extension origin', async () => {
+    const { openPairingWindow, claimPairing, isOriginAllowed } = await import('./pairing')
+    openPairingWindow()
+    const res = await claimPairing('moz-extension://abc')
+    expect(res?.token).toHaveLength(64)
+    expect(isOriginAllowed('moz-extension://abc')).toBe(true)
+  })
+
   it('rotate clears the allowlist and changes the token', async () => {
     const { openPairingWindow, claimPairing, rotateCaptureToken, isOriginAllowed } =
       await import('./pairing')
diff --git a/apps/desktop/src/main/capture/pairing.ts b/apps/desktop/src/main/capture/pairing.ts
index 0851303b8..919981211 100644
--- a/apps/desktop/src/main/capture/pairing.ts
+++ b/apps/desktop/src/main/capture/pairing.ts
@@ -1,6 +1,7 @@
 import { randomBytes } from 'node:crypto'
 import keytar from 'keytar'
 import { store } from '../store'
+import { isExtensionOrigin } from './auth'
 
 const SERVICE = 'com.memry.capture'
 const ACCOUNT = 'pairing-token'
@@ -71,7 +72,7 @@ export function isPairingWindowOpen(now = Date.now()): boolean {
 
 export async function claimPairing(origin: string): Promise<{ token: string } | null> {
   if (!isPairingWindowOpen()) return null
-  if (!origin.startsWith('chrome-extension://')) return null
+  if (!isExtensionOrigin(origin)) return null
   const list = allowlist()
   if (!list.includes(origin)) store.set(ALLOWLIST_KEY, [...list, origin])
   claimWindowUntil = 0 // single claim closes the window
diff --git a/apps/desktop/src/main/capture/server.test.ts b/apps/desktop/src/main/capture/server.test.ts
index 59b20da76..7bd1e245d 100644
--- a/apps/desktop/src/main/capture/server.test.ts
+++ b/apps/desktop/src/main/capture/server.test.ts
@@ -168,6 +168,17 @@ describe('capture server', () => {
     expect((await r.json()).error).toBe('origin-not-allowed')
   })
 
+  it('/pair/request for an allowlisted Firefox moz-extension origin → 200 already-paired', async () => {
+    origins.add('moz-extension://ext-firefox')
+    const r = await req(port, '/pair/request', {
+      method: 'POST',
+      headers: { Origin: 'moz-extension://ext-firefox', 'X-Memry-Capture': '1' }
+    })
+    expect(r.status).toBe(200)
+    expect((await r.json()).status).toBe('already-paired')
+    expect(openPairingWindowMock).toHaveBeenCalledTimes(1)
+  })
+
   it('/pair/request missing X-Memry-Capture header → 401 missing-capture-header', async () => {
     const r = await req(port, '/pair/request', {
       method: 'POST',
diff --git a/apps/desktop/src/main/capture/server.ts b/apps/desktop/src/main/capture/server.ts
index 93d4cfa2f..2ef9f4c68 100644
--- a/apps/desktop/src/main/capture/server.ts
+++ b/apps/desktop/src/main/capture/server.ts
@@ -9,7 +9,7 @@ import {
   openPairingWindow,
   unpairCapture
 } from './pairing'
-import { validateCaptureRequest } from './auth'
+import { validateCaptureRequest, isExtensionOrigin } from './auth'
 import { createLogger } from '../lib/logger'
 
 const log = createLogger('Capture:Server')
@@ -77,7 +77,7 @@ async function handle(req: http.IncomingMessage, res: http.ServerResponse): Prom
       json(res, 400, { error: 'missing-origin' })
       return
     }
-    if (!origin.startsWith('chrome-extension://')) {
+    if (!isExtensionOrigin(origin)) {
       json(res, 403, { error: 'origin-not-allowed' })
       return
     }
diff --git a/apps/docs/src/user-guide/inbox/capturing.md b/apps/docs/src/user-guide/inbox/capturing.md
index 40c9bfea9..70f2097cf 100644
--- a/apps/docs/src/user-guide/inbox/capturing.md
+++ b/apps/docs/src/user-guide/inbox/capturing.md
@@ -64,6 +64,11 @@ If voice transcription setup is incomplete, memrynote takes you to AI settings b
 The memrynote browser extension captures the page you're reading straight into your inbox. Web clips
 appear under the **clips** content type filter.
 
+### Supported browsers
+
+The extension is a single cross-browser build that runs on Chrome, Edge, and Firefox (version 140 or
+newer). Pairing and all capture modes work the same on each.
+
 ### Pairing
 
 The extension talks to the desktop app over a local loopback connection — nothing leaves your
diff --git a/apps/extension/README.md b/apps/extension/README.md
index 190789578..0432ae51e 100644
--- a/apps/extension/README.md
+++ b/apps/extension/README.md
@@ -20,6 +20,37 @@ pnpm --filter @memry/extension lint
 3. **Load unpacked** → select `apps/extension/.output/chrome-mv3`.
 4. Keep the load path stable so the extension ID (and pairing) survives reloads.
 
+## Load temporary add-on in Firefox
+
+Same WXT source, MV3 build (`--mv3` keeps `browser.action`/`host_permissions`
+matching the Chrome source). Stable id comes from `browser_specific_settings.gecko`.
+
+1. `pnpm --filter @memry/extension build:firefox`
+2. Firefox → `about:debugging#/runtime/this-firefox`.
+3. **Load Temporary Add-on…** → select `apps/extension/.output/firefox-mv3/manifest.json`.
+4. Requires Firefox ≥ 140 (`strict_min_version`, the floor for AMO's
+   `data_collection_permissions`). The `Ctrl+Shift+S` command may
+   clash with Firefox's screenshot shortcut — rebind it under
+   `about:addons → ⚙ → Manage Extension Shortcuts` if it doesn't fire; the popup
+   button works regardless.
+
+`pnpm --filter @memry/extension dev:firefox` launches a dev Firefox with
+auto-reload (via web-ext). `zip:firefox` produces a signable artifact when you
+take it to AMO.
+
+## Load unpacked in Edge
+
+Edge is Chromium, so the Chrome build already runs on it (same
+`chrome-extension://` origin → capture pairing works unchanged). The `:edge`
+scripts just produce a separately-named artifact for the Edge Add-ons store.
+
+1. `pnpm --filter @memry/extension build:edge`
+2. Edge → `edge://extensions` → enable **Developer mode**.
+3. **Load unpacked** → select `apps/extension/.output/edge-mv3`.
+
+`zip:edge` produces `.output/*-edge.zip` for submission to the Microsoft Edge
+Add-ons store.
+
 ## Manual QA (the Phase-3 acceptance gate — human-required)
 
 Run the desktop app first: `pnpm dev`.
diff --git a/apps/extension/package.json b/apps/extension/package.json
index 591b7e04c..5d73f8467 100644
--- a/apps/extension/package.json
+++ b/apps/extension/package.json
@@ -5,8 +5,14 @@
   "type": "module",
   "scripts": {
     "dev": "wxt",
+    "dev:firefox": "wxt -b firefox --mv3",
+    "dev:edge": "wxt -b edge",
     "build": "wxt build",
+    "build:firefox": "wxt build -b firefox --mv3",
+    "build:edge": "wxt build -b edge",
     "zip": "wxt zip",
+    "zip:firefox": "wxt zip -b firefox --mv3",
+    "zip:edge": "wxt zip -b edge",
     "submit": "wxt submit --chrome-zip .output/*-chrome.zip",
     "release": "pnpm version --tag-version-prefix=extension-v --message \"chore(extension): release v%s\" && git push --follow-tags",
     "typecheck": "wxt prepare && tsc --noEmit",
diff --git a/apps/extension/wxt.config.ts b/apps/extension/wxt.config.ts
index 889592e06..161a109f2 100644
--- a/apps/extension/wxt.config.ts
+++ b/apps/extension/wxt.config.ts
@@ -15,6 +15,22 @@ export default defineConfig({
         suggested_key: { default: 'Ctrl+Shift+S', mac: 'Command+Shift+S' },
         description: 'Capture this page to MemryNote'
       }
+    },
+    // ponytail: stable gecko id → storage.local pairing token survives reloads; required for AMO.
+    // Firefox builds target MV3 (--mv3) so browser.action/host_permissions match the Chrome source unchanged.
+    browser_specific_settings: {
+      // min versions = where data_collection_permissions is honored (FF 140 / Android 142),
+      // not where MV3 starts — avoids the AMO "key ignored below this version" warning.
+      gecko: {
+        id: 'web-clipper@memrynote.com',
+        strict_min_version: '140.0',
+        // AMO requires this for new add-ons (since 2025-11-03). Captures go only to the
+        // user's own desktop app on 127.0.0.1 — nothing is collected by the developer.
+        data_collection_permissions: { required: ['none'] }
+      },
+      gecko_android: {
+        strict_min_version: '142.0'
+      }
     }
   },
   vite: () => ({