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+# idfoto — Firefox Extension Port Design
+
+Port the existing Chrome MV3 extension to Firefox. Shared TypeScript source, separate manifests, separate build outputs. No code changes to components, popup, or content script.
+
+## Scope
+
+- Firefox-specific `manifest.json`
+- WASM loading compatibility (dynamic import for Firefox background script)
+- Second webpack config for Firefox build target
+- npm scripts for building both browsers
+
+## What Stays the Same
+
+All TypeScript source files are shared between Chrome and Firefox:
+- `src/service-worker/` — all files (with one environment check for WASM loading)
+- `src/popup/` — all components, styles, HTML
+- `src/content/` — detector, fill, icon, capture
+- `src/setup/` — setup wizard
+- `src/shared/` — types, messages
+- `setup.html` — init wizard
+
+Firefox supports the `chrome.*` namespace for WebExtension APIs, so no `browser.*` polyfill is needed. All Chrome API calls (`chrome.runtime.sendMessage`, `chrome.storage.local`, `chrome.tabs`, etc.) work as-is.
+
+## Manifest Differences
+
+### Chrome (`manifest.json` — existing)
+
+```json
+{
+  "manifest_version": 3,
+  "background": {
+    "service_worker": "service-worker.js",
+    "type": "module"
+  }
+}
+```
+
+### Firefox (`manifest.firefox.json` — new)
+
+```json
+{
+  "manifest_version": 3,
+  "name": "idfoto",
+  "version": "0.1.0",
+  "description": "Two-factor encrypted password manager",
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "idfoto@adlee.work",
+      "strict_min_version": "128.0"
+    }
+  },
+  "permissions": ["storage", "activeTab", "clipboardWrite"],
+  "host_permissions": ["<all_urls>"],
+  "background": {
+    "scripts": ["service-worker.js"]
+  },
+  "action": {
+    "default_popup": "popup.html",
+    "default_icon": {
+      "16": "icons/icon-16.png",
+      "48": "icons/icon-48.png",
+      "128": "icons/icon-128.png"
+    }
+  },
+  "content_scripts": [{
+    "matches": ["<all_urls>"],
+    "js": ["content.js"],
+    "run_at": "document_idle"
+  }],
+  "content_security_policy": {
+    "extension_pages": "script-src 'self' 'wasm-unsafe-eval'; object-src 'self'"
+  },
+  "web_accessible_resources": [{
+    "resources": ["setup.html", "setup.js", "styles.css", "idfoto_wasm_bg.wasm", "idfoto_wasm.js"]
+  }]
+}
+```
+
+Key differences from Chrome manifest:
+- `browser_specific_settings.gecko.id` — required for Firefox, uses email-style ID
+- `browser_specific_settings.gecko.strict_min_version` — Firefox 128+ for stable MV3 support
+- `background.scripts` instead of `background.service_worker` + `type: module` — Firefox MV3 background scripts are NOT service workers, they're persistent scripts
+- `web_accessible_resources` — Firefox doesn't use `matches` field in the resource entries
+
+## WASM Loading
+
+The service worker `index.ts` currently uses `initSync` with `chrome.runtime.getURL` because Chrome MV3 service workers don't support dynamic `import()`. Firefox background scripts DO support `import()`.
+
+Add an environment check to `index.ts`:
+
+```typescript
+async function initWasm(): Promise<WasmModule> {
+  if (wasm) return wasm;
+
+  if (typeof ServiceWorkerGlobalScope !== 'undefined') {
+    // Chrome MV3: service worker context — use initSync
+    const wasmResponse = await fetch(chrome.runtime.getURL('idfoto_wasm_bg.wasm'));
+    const wasmBytes = await wasmResponse.arrayBuffer();
+    initSync({ module: new WebAssembly.Module(wasmBytes) });
+  } else {
+    // Firefox: background script context — dynamic import works
+    const wasmUrl = chrome.runtime.getURL('idfoto_wasm_bg.wasm');
+    await initDefault(wasmUrl);
+  }
+
+  vault.setWasm(wasmBindings);
+  wasm = wasmBindings;
+  wasmReady = true;
+  return wasm;
+}
+```
+
+This uses the static import of `initSync` and the default export (`initDefault`) from the WASM glue, branching on runtime environment. Both paths end with the same `wasmBindings` module reference.
+
+## Build Pipeline
+
+### New file: `extension/webpack.firefox.config.js`
+
+Identical to `webpack.config.js` except:
+- Output directory: `dist-firefox/` instead of `dist/`
+- CopyPlugin copies `manifest.firefox.json` as `manifest.json` (instead of `manifest.json`)
+
+### Updated `extension/package.json` scripts
+
+```json
+{
+  "scripts": {
+    "build": "webpack --mode production",
+    "build:firefox": "webpack --config webpack.firefox.config.js --mode production",
+    "build:all": "npm run build:wasm && npm run build && npm run build:firefox",
+    "dev": "webpack --mode development --watch",
+    "dev:firefox": "webpack --config webpack.firefox.config.js --mode development --watch",
+    "build:wasm": "wasm-pack build ../crates/idfoto-wasm --target web --out-dir ../../extension/wasm"
+  }
+}
+```
+
+### Output structure
+
+```
+extension/
+├── dist/              # Chrome build (existing)
+│   ├── service-worker.js
+│   ├── popup.js
+│   ├── content.js
+│   ├── setup.js
+│   ├── manifest.json  # Chrome manifest
+│   └── ...
+├── dist-firefox/      # Firefox build (new)
+│   ├── service-worker.js
+│   ├── popup.js
+│   ├── content.js
+│   ├── setup.js
+│   ├── manifest.json  # Firefox manifest (copied from manifest.firefox.json)
+│   └── ...
+└── wasm/              # Shared WASM (same for both)
+```
+
+## Testing
+
+### Load in Firefox
+
+1. Open `about:debugging#/runtime/this-firefox`
+2. Click "Load Temporary Add-on..."
+3. Select `extension/dist-firefox/manifest.json`
+4. Extension appears in toolbar
+
+### Test matrix
+
+Same as Chrome — all features should work identically:
+- Setup wizard (`setup.html`)
+- Unlock with passphrase
+- Entry list, search, group filtering
+- Entry detail with TOTP countdown
+- Add/edit/delete entries
+- Autofill via field icon
+- Credential capture (if enabled)
+- Settings view
+
+### Firefox-specific checks
+
+- WASM loads correctly (background script, not service worker)
+- master_key persists longer (background script stays alive)
+- Popup dimensions render correctly
+- Content script injection works on all pages
+
+## .gitignore
+
+Add `extension/dist-firefox/` to `.gitignore`.
+
+## Non-Goals
+
+- Firefox for Android (different extension API surface)
+- Publishing to addons.mozilla.org (manual for now)
+- Automated cross-browser testing
+- Shared webpack config with conditional logic (two separate configs is clearer)