feat: add Firefox support with webextension-polyfill

Implemented cross-browser compatibility for the extension:

- Installed webextension-polyfill for unified browser.* API
- Replaced all chrome.* API calls with browser.* imports
- Updated build system to output both chrome/ and firefox/ directories
- Created Firefox-specific manifest with browser_specific_settings

docs/git-history.json

···
 [
   {
+    "hash": "603cf0a187850664336a12c9e5cbb49038906f53",
+    "short_hash": "603cf0a",
+    "author": "Ariel M. Lighty",
+    "date": "2025-12-27T22:42:43-05:00",
+    "message": "fix: CORS for extension credentialed requests\n\nUpdated CORS headers to support credentials from Chrome extensions:\n- Added getCorsHeaders() to detect chrome-extension:// origins\n- Changed from wildcard Access-Control-Allow-Origin to specific origin\n- Added Access-Control-Allow-Credentials: true for credentialed requests\n- Updated session endpoint to pass event for CORS header detection",
+    "files_changed": 4
+  },
+  {
     "hash": "bd3aabb75abb1875aef125610fcdccb14967a8e3",
     "short_hash": "bd3aabb",
     "author": "Ariel M. Lighty",
···
     "files_changed": 5
   },
   {
-    "hash": "d07180cd3a19328b82b35118e525b59d4e2e060b",
-    "short_hash": "d07180c",
+    "hash": "bd3aabb75abb1875aef125610fcdccb14967a8e3",
+    "short_hash": "bd3aabb",
     "author": "Ariel M. Lighty",
-    "date": "2025-12-27T18:38:39-05:00",
-    "message": "feat: add Tailwind CSS to extension\n\nReplaced 299 lines of vanilla CSS with Tailwind for design consistency with web app. Production build minified to 13KB.",
-    "files_changed": 9
+    "date": "2025-12-27T22:10:11-05:00",
+    "message": "fix: extension dark mode and build mode messaging\n\n- Changed darkMode from 'class' to 'media' for automatic system preference detection\n- Made server offline message conditional on build mode (dev vs prod)\n- Hide dev server instructions in production builds",
+    "files_changed": 5
   },
   {
     "hash": "d07180cd3a19328b82b35118e525b59d4e2e060b",
···
     "files_changed": 6
   },
   {
-    "hash": "fcf682bb8969aca108262348e7e17531077713be",
-    "short_hash": "fcf682b",
+    "hash": "2a163c5f033a79324b100a236ea26c905909bfc6",
+    "short_hash": "2a163c5",
     "author": "Ariel M. Lighty",
-    "date": "2025-12-27T15:48:44-05:00",
-    "message": "docs: improve decision graph workflow with lifecycle management\n\nUpdated CLAUDE.md with comprehensive node lifecycle management:\n- Added node status transitions (pending → in_progress → completed)\n- Correct orphan detection commands (awk instead of cut)\n- Common mistakes section with examples\n- Enhanced audit checklist with status verification\n- Verification workflow after node creation\n\nAlso updated extension popup with ATmosphere branding.\n\nDecision graph now at 331 nodes, 332 edges - all orphans resolved.",
-    "files_changed": 4
+    "date": "2025-12-27T15:49:08-05:00",
+    "message": "docs: update decision graph after documentation improvements",
+    "files_changed": 2
   },
   {
     "hash": "fcf682bb8969aca108262348e7e17531077713be",

docs/graph-data.json

···
       "created_at": "2025-12-27T22:41:38.430661200-05:00",
       "updated_at": "2025-12-27T22:41:48.981429600-05:00",
       "metadata_json": "{\"branch\":\"master\",\"confidence\":95}"
+    },
+    {
+      "id": 366,
+      "change_id": "77b7ed7e-a113-41f6-a677-50d376f3f008",
+      "node_type": "outcome",
+      "title": "Committed CORS fixes to git",
+      "description": null,
+      "status": "completed",
+      "created_at": "2025-12-27T22:42:49.037783-05:00",
+      "updated_at": "2025-12-27T22:42:54.162857-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"commit\":\"603cf0a\",\"confidence\":95}"
+    },
+    {
+      "id": 367,
+      "change_id": "df6abf7a-e7a4-45f3-8485-b933319416d9",
+      "node_type": "goal",
+      "title": "Create Firefox-compatible version of Twitter scraper extension",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T18:09:33.241860800-05:00",
+      "updated_at": "2025-12-28T18:09:33.241860800-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":85,\"prompt\":\"let's make the extension have a firefox compatible version too.\"}"
+    },
+    {
+      "id": 368,
+      "change_id": "79721edf-aa05-4580-8c28-7d20941ef155",
+      "node_type": "observation",
+      "title": "Current extension uses Manifest V3 with Chrome-specific APIs",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T18:10:08.441348100-05:00",
+      "updated_at": "2025-12-28T18:10:08.441348100-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":95}"
+    },
+    {
+      "id": 369,
+      "change_id": "783841d0-c096-48f6-be18-193a9dcc7d4b",
+      "node_type": "observation",
+      "title": "Firefox compatibility analysis: Extension uses chrome.* APIs (runtime.sendMessage, storage.local, tabs.query/sendMessage), MV3 service worker. Firefox supports MV3 but has differences. Options: 1) Use webextension-polyfill for cross-browser, 2) Dual manifests (MV3 Chrome + MV2 Firefox), 3) Keep MV3 for both with minimal changes. Current build outputs to dist/chrome only.",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T18:10:48.087066800-05:00",
+      "updated_at": "2025-12-28T18:10:48.087066800-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":90}"
+    },
+    {
+      "id": 370,
+      "change_id": "fd2d5b63-c26c-4592-89a6-3ccb4234c3c6",
+      "node_type": "decision",
+      "title": "Choose Firefox compatibility approach: webextension-polyfill, dual manifests, or minimal MV3 changes",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T18:10:50.375270400-05:00",
+      "updated_at": "2025-12-28T18:10:50.375270400-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":80}"
+    },
+    {
+      "id": 371,
+      "change_id": "159906da-984f-4a1d-a1a6-98e0fc0cf369",
+      "node_type": "option",
+      "title": "Use webextension-polyfill library for unified cross-browser API",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T18:11:05.947924200-05:00",
+      "updated_at": "2025-12-28T18:11:05.947924200-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":85}"
+    },
+    {
+      "id": 372,
+      "change_id": "df5e42e6-53c1-4b30-8b6f-f2385cd9e247",
+      "node_type": "option",
+      "title": "Dual manifests: MV3 for Chrome, MV2 for Firefox with separate builds",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T18:11:08.179938100-05:00",
+      "updated_at": "2025-12-28T18:11:08.179938100-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":85}"
+    },
+    {
+      "id": 373,
+      "change_id": "7bb58202-7a9b-4e8b-8b9e-927e5106bce7",
+      "node_type": "option",
+      "title": "Keep MV3 for both browsers with minimal manifest tweaks",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T18:11:10.370113600-05:00",
+      "updated_at": "2025-12-28T18:11:10.370113600-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":85}"
+    },
+    {
+      "id": 374,
+      "change_id": "d41b29e0-cd48-4dac-a6c8-c6179612702e",
+      "node_type": "outcome",
+      "title": "Chose webextension-polyfill approach. Provides unified browser.* API, Promise-based, future-proof MV3 for both browsers, +20KB but cleaner codebase",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T19:04:24.676770900-05:00",
+      "updated_at": "2025-12-28T19:04:24.676770900-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":95}"
+    },
+    {
+      "id": 375,
+      "change_id": "5bb34b8b-aec4-4f84-993e-eb9bf7a2d13f",
+      "node_type": "action",
+      "title": "Installing webextension-polyfill and updating source files to use browser.* API",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T19:08:14.642882400-05:00",
+      "updated_at": "2025-12-28T19:08:14.642882400-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":90}"
+    },
+    {
+      "id": 376,
+      "change_id": "644181ee-5a44-4967-9657-e9dd5f648c5e",
+      "node_type": "outcome",
+      "title": "Successfully implemented Firefox compatibility with webextension-polyfill. Both Chrome and Firefox builds compile successfully. Chrome uses service_worker (MV3), Firefox uses scripts array with browser_specific_settings. All chrome.* API calls replaced with browser.* imports.",
+      "description": null,
+      "status": "pending",
+      "created_at": "2025-12-28T19:14:22.309457600-05:00",
+      "updated_at": "2025-12-28T19:14:22.309457600-05:00",
+      "metadata_json": "{\"branch\":\"master\",\"confidence\":95}"
     }
   ],
   "edges": [
···
       "weight": 1.0,
       "rationale": "CORS fix completed",
       "created_at": "2025-12-27T22:41:44.160528300-05:00"
+    },
+    {
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+      "from_node_id": 360,
+      "to_node_id": 366,
+      "from_change_id": "706d5a7f-08ed-43f7-aee5-0bed28d9402a",
+      "to_change_id": "77b7ed7e-a113-41f6-a677-50d376f3f008",
+      "edge_type": "leads_to",
+      "weight": 1.0,
+      "rationale": "Git commit for CORS fixes",
+      "created_at": "2025-12-27T22:42:51.663598100-05:00"
+    },
+    {
+      "id": 365,
+      "from_node_id": 367,
+      "to_node_id": 368,
+      "from_change_id": "df6abf7a-e7a4-45f3-8485-b933319416d9",
+      "to_change_id": "79721edf-aa05-4580-8c28-7d20941ef155",
+      "edge_type": "leads_to",
+      "weight": 1.0,
+      "rationale": "Analysis step for Firefox compatibility",
+      "created_at": "2025-12-28T18:10:09.484445500-05:00"
+    },
+    {
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+      "from_node_id": 368,
+      "to_node_id": 369,
+      "from_change_id": "79721edf-aa05-4580-8c28-7d20941ef155",
+      "to_change_id": "783841d0-c096-48f6-be18-193a9dcc7d4b",
+      "edge_type": "leads_to",
+      "weight": 1.0,
+      "rationale": "Detailed analysis of compatibility issues",
+      "created_at": "2025-12-28T18:10:49.163552300-05:00"
+    },
+    {
+      "id": 367,
+      "from_node_id": 369,
+      "to_node_id": 370,
+      "from_change_id": "783841d0-c096-48f6-be18-193a9dcc7d4b",
+      "to_change_id": "fd2d5b63-c26c-4592-89a6-3ccb4234c3c6",
+      "edge_type": "leads_to",
+      "weight": 1.0,
+      "rationale": "Need to decide implementation strategy",
+      "created_at": "2025-12-28T18:10:51.434960600-05:00"
+    },
+    {
+      "id": 368,
+      "from_node_id": 370,
+      "to_node_id": 371,
+      "from_change_id": "fd2d5b63-c26c-4592-89a6-3ccb4234c3c6",
+      "to_change_id": "159906da-984f-4a1d-a1a6-98e0fc0cf369",
+      "edge_type": "leads_to",
+      "weight": 1.0,
+      "rationale": "Option A",
+      "created_at": "2025-12-28T18:11:07.060637-05:00"
+    },
+    {
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+      "from_node_id": 370,
+      "to_node_id": 372,
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+      "edge_type": "leads_to",
+      "weight": 1.0,
+      "rationale": "Option B",
+      "created_at": "2025-12-28T18:11:09.223792400-05:00"
+    },
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+      "from_node_id": 370,
+      "to_node_id": 373,
+      "from_change_id": "fd2d5b63-c26c-4592-89a6-3ccb4234c3c6",
+      "to_change_id": "7bb58202-7a9b-4e8b-8b9e-927e5106bce7",
+      "edge_type": "leads_to",
+      "weight": 1.0,
+      "rationale": "Option C",
+      "created_at": "2025-12-28T18:11:11.439827800-05:00"
+    },
+    {
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+      "from_node_id": 370,
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+      "rationale": "User selected option 1",
+      "created_at": "2025-12-28T19:04:26.708742600-05:00"
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     }
   ]
 }

packages/extension/FIREFOX.md

···
+# Firefox Extension Installation Guide
+
+The ATlast Importer extension now supports both Chrome and Firefox!
+
+## Building for Firefox
+
+The build system automatically creates both Chrome and Firefox versions:
+
+```bash
+pnpm run build        # Development build for both browsers
+pnpm run build:prod   # Production build for both browsers
+```
+
+Output directories:
+- `dist/chrome/` - Chrome/Edge version (Manifest V3 with service worker)
+- `dist/firefox/` - Firefox version (Manifest V3 with scripts array)
+
+## Installing in Firefox (Development)
+
+### Option 1: Temporary Installation (for testing)
+
+1. Open Firefox
+2. Navigate to `about:debugging#/runtime/this-firefox`
+3. Click "Load Temporary Add-on..."
+4. Navigate to `packages/extension/dist/firefox/`
+5. Select the `manifest.json` file
+
+**Note:** Temporary extensions are removed when Firefox restarts.
+
+### Option 2: Loading from ZIP (for distribution)
+
+1. Build the production version:
+   ```bash
+   pnpm run build:prod
+   pnpm run package:firefox
+   ```
+
+2. This creates `dist/firefox.zip`
+
+3. For testing:
+   - Go to `about:debugging#/runtime/this-firefox`
+   - Click "Load Temporary Add-on..."
+   - Select the `firefox.zip` file
+
+4. For publishing:
+   - Submit `firefox.zip` to [addons.mozilla.org](https://addons.mozilla.org/developers/)
+
+## Key Differences from Chrome Version
+
+### Manifest Differences
+
+**Chrome (`manifest.chrome.json`):**
+```json
+{
+  "manifest_version": 3,
+  "background": {
+    "service_worker": "background/service-worker.js",
+    "type": "module"
+  }
+}
+```
+
+**Firefox (`manifest.firefox.json`):**
+```json
+{
+  "manifest_version": 3,
+  "background": {
+    "scripts": ["background/service-worker.js"],
+    "type": "module"
+  },
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "[e-mail]",
+      "strict_min_version": "109.0"
+    }
+  }
+}
+```
+
+### Cross-Browser Compatibility
+
+- All code uses `webextension-polyfill` library
+- Chrome-specific `chrome.*` APIs replaced with unified `browser.*` API
+- Promise-based instead of callback-based
+- Single codebase works across both browsers
+
+### Requirements
+
+- **Firefox:** Version 109+ (for Manifest V3 support)
+- **Chrome/Edge:** Latest version
+
+## Testing
+
+After loading the extension in Firefox:
+
+1. Navigate to Twitter/X Following page (e.g., `https://twitter.com/username/following`)
+2. Click the extension icon in the toolbar
+3. The popup should show "Ready to scan" state
+4. Click "Start Scan" to scrape usernames
+5. Click "Open on ATlast" to upload results
+
+## Debugging
+
+### View Console Logs
+
+**Background Script:**
+- Go to `about:debugging#/runtime/this-firefox`
+- Find "ATlast Importer" in the list
+- Click "Inspect"
+
+**Popup:**
+- Right-click extension icon → "Inspect Extension"
+
+**Content Script:**
+- Open DevTools on Twitter/X page (F12)
+- Look for `[ATlast]` prefixed logs in Console
+
+### Common Issues
+
+1. **Extension not loading:**
+   - Check Firefox version is 109+
+   - Ensure manifest.json is valid
+   - Check browser console for errors
+
+2. **Scan not starting:**
+   - Verify you're on Twitter/X Following page
+   - Check content script is injected (look for console logs)
+   - Ensure page is fully loaded
+
+3. **"Server offline" message:**
+   - Make sure dev server is running (`netlify dev`)
+   - Check API URL in extension settings
+
+## Packaging for Distribution
+
+Create production builds for both browsers:
+
+```bash
+pnpm run package:prod
+```
+
+This creates:
+- `dist/chrome.zip` - Ready for Chrome Web Store
+- `dist/firefox.zip` - Ready for Firefox Add-ons
+
+## Development Workflow
+
+```bash
+# Watch mode (auto-rebuild on changes)
+pnpm run dev
+
+# In Firefox:
+# 1. about:debugging → Reload extension after each rebuild
+# 2. Or use web-ext for auto-reload:
+
+npx web-ext run --source-dir=dist/firefox
+```
+
+## Differences You Might Notice
+
+1. **Background page persistence:**
+   - Chrome: Service worker (non-persistent)
+   - Firefox: Scripts array (similar behavior in MV3)
+
+2. **API behavior:**
+   - Firefox: Native Promise support
+   - Chrome: Promises via polyfill
+
+3. **Extension ID:**
+   - Chrome: Auto-generated
+   - Firefox: Explicitly set as `[e-mail]`
+
+Both versions use the same source code and should behave identically!

packages/extension/build.js

···
 console.log(`🔗 API URL: ${ATLAST_API_URL}`);
 
 // Clean dist directory
-const distDir = path.join(__dirname, 'dist', 'chrome');
-if (fs.existsSync(distDir)) {
-  fs.rmSync(distDir, { recursive: true });
+const distBaseDir = path.join(__dirname, 'dist');
+if (fs.existsSync(distBaseDir)) {
+  fs.rmSync(distBaseDir, { recursive: true });
 }
-fs.mkdirSync(distDir, { recursive: true });
+fs.mkdirSync(distBaseDir, { recursive: true });
 
 // Build configuration base
 const buildConfigBase = {
···
     '__ATLAST_API_URL__': JSON.stringify(ATLAST_API_URL),
     '__BUILD_MODE__': JSON.stringify(mode),
   },
+  // Include webextension-polyfill in the bundle
+  external: [],
 };
 
-// Build scripts
-const scripts = [
-  {
-    ...buildConfigBase,
-    entryPoints: ['src/content/index.ts'],
-    outfile: path.join(distDir, 'content', 'index.js'),
-  },
-  {
-    ...buildConfigBase,
-    entryPoints: ['src/background/service-worker.ts'],
-    outfile: path.join(distDir, 'background', 'service-worker.js'),
-  },
-  {
-    ...buildConfigBase,
-    entryPoints: ['src/popup/popup.ts'],
-    outfile: path.join(distDir, 'popup', 'popup.js'),
-  },
-];
+// Build scripts for a specific browser
+function getScripts(browser) {
+  const distDir = path.join(distBaseDir, browser);
+  return [
+    {
+      ...buildConfigBase,
+      entryPoints: ['src/content/index.ts'],
+      outfile: path.join(distDir, 'content', 'index.js'),
+    },
+    {
+      ...buildConfigBase,
+      entryPoints: ['src/background/service-worker.ts'],
+      outfile: path.join(distDir, 'background', 'service-worker.js'),
+    },
+    {
+      ...buildConfigBase,
+      entryPoints: ['src/popup/popup.ts'],
+      outfile: path.join(distDir, 'popup', 'popup.js'),
+    },
+  ];
+}
 
 // Build function
 async function build() {
   try {
-    console.log('🔨 Building extension...');
+    console.log('🔨 Building extension for Chrome and Firefox...');
+
+    const browsers = ['chrome', 'firefox'];
 
-    // Build all scripts
-    for (const config of scripts) {
-      if (watch) {
-        const ctx = await esbuild.context(config);
-        await ctx.watch();
-        console.log(`👀 Watching ${path.basename(config.entryPoints[0])}...`);
-      } else {
-        await esbuild.build(config);
-        console.log(`✅ Built ${path.basename(config.entryPoints[0])}`);
+    for (const browser of browsers) {
+      console.log(`\n📦 Building ${browser} version...`);
+      const scripts = getScripts(browser);
+
+      // Build all scripts
+      for (const config of scripts) {
+        if (watch) {
+          const ctx = await esbuild.context(config);
+          await ctx.watch();
+          console.log(`👀 Watching ${browser}/${path.basename(config.entryPoints[0])}...`);
+        } else {
+          await esbuild.build(config);
+          console.log(`✅ Built ${browser}/${path.basename(config.entryPoints[0])}`);
+        }
       }
-    }
 
-    // Copy static files
-    copyStaticFiles();
+      // Copy static files
+      copyStaticFiles(browser);
 
-    // Process CSS with Tailwind
-    await processCSS();
+      // Process CSS with Tailwind
+      await processCSS(browser);
+    }
 
     if (!watch) {
-      console.log('✨ Build complete!');
+      console.log('\n✨ Build complete for both browsers!');
     }
   } catch (error) {
     console.error('❌ Build failed:', error);
···
 }
 
 // Process CSS with PostCSS (Tailwind + Autoprefixer)
-async function processCSS() {
+async function processCSS(browser) {
   const cssPath = path.join(__dirname, 'src/popup/popup.css');
+  const distDir = path.join(distBaseDir, browser);
   const outputPath = path.join(distDir, 'popup/popup.css');
 
   const css = fs.readFileSync(cssPath, 'utf8');
···
 }
 
 // Copy static files
-function copyStaticFiles() {
+function copyStaticFiles(browser) {
+  const distDir = path.join(distBaseDir, browser);
+
   const filesToCopy = [
-    { from: 'manifest.json', to: 'manifest.json' },
+    { from: `manifest.${browser}.json`, to: 'manifest.json', fallback: 'manifest.json' },
     { from: 'src/popup/popup.html', to: 'popup/popup.html' },
   ];
 
   for (const file of filesToCopy) {
-    const srcPath = path.join(__dirname, file.from);
+    // Try to use browser-specific file first, fall back to default
+    let srcPath = path.join(__dirname, file.from);
+    if (file.fallback && !fs.existsSync(srcPath)) {
+      srcPath = path.join(__dirname, file.fallback);
+    }
     const destPath = path.join(distDir, file.to);
 
     // Create directory if it doesn't exist

packages/extension/manifest.chrome.json

···
+{
+  "manifest_version": 3,
+  "name": "ATlast Importer",
+  "version": "1.0.0",
+  "description": "Import your Twitter/X follows to find them on Bluesky",
+  "permissions": [
+    "activeTab",
+    "storage"
+  ],
+  "host_permissions": [
+    "https://twitter.com/*",
+    "https://x.com/*",
+    "http://127.0.0.1:8888/*",
+    "http://localhost:8888/*",
+    "https://atlast.byarielm.fyi/*"
+  ],
+  "background": {
+    "service_worker": "background/service-worker.js",
+    "type": "module"
+  },
+  "content_scripts": [
+    {
+      "matches": [
+        "https://twitter.com/*",
+        "https://x.com/*"
+      ],
+      "js": ["content/index.js"],
+      "run_at": "document_idle"
+    }
+  ],
+  "action": {
+    "default_popup": "popup/popup.html",
+    "default_icon": {
+      "16": "assets/icon-16.png",
+      "48": "assets/icon-48.png",
+      "128": "assets/icon-128.png"
+    }
+  },
+  "icons": {
+    "16": "assets/icon-16.png",
+    "48": "assets/icon-48.png",
+    "128": "assets/icon-128.png"
+  }
+}

packages/extension/manifest.firefox.json

···
+{
+  "manifest_version": 3,
+  "name": "ATlast Importer",
+  "version": "1.0.0",
+  "description": "Import your Twitter/X follows to find them on Bluesky",
+  "permissions": [
+    "activeTab",
+    "storage"
+  ],
+  "host_permissions": [
+    "https://twitter.com/*",
+    "https://x.com/*",
+    "http://127.0.0.1:8888/*",
+    "http://localhost:8888/*",
+    "https://atlast.byarielm.fyi/*"
+  ],
+  "background": {
+    "scripts": ["background/service-worker.js"],
+    "type": "module"
+  },
+  "content_scripts": [
+    {
+      "matches": [
+        "https://twitter.com/*",
+        "https://x.com/*"
+      ],
+      "js": ["content/index.js"],
+      "run_at": "document_idle"
+    }
+  ],
+  "action": {
+    "default_popup": "popup/popup.html",
+    "default_icon": {
+      "16": "assets/icon-16.png",
+      "48": "assets/icon-48.png",
+      "128": "assets/icon-128.png"
+    }
+  },
+  "icons": {
+    "16": "assets/icon-16.png",
+    "48": "assets/icon-48.png",
+    "128": "assets/icon-128.png"
+  },
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "[e-mail]",
+      "strict_min_version": "109.0"
+    }
+  }
+}

packages/extension/package.json

···
     "build:prod": "node build.js --prod",
     "dev": "node build.js --watch",
     "package:chrome": "cd dist/chrome && zip -r ../chrome.zip .",
-    "package:prod": "npm run build:prod && npm run package:chrome"
+    "package:firefox": "cd dist/firefox && zip -r ../firefox.zip .",
+    "package:all": "pnpm run package:chrome && pnpm run package:firefox",
+    "package:prod": "pnpm run build:prod && pnpm run package:all"
   },
   "dependencies": {
-    "@atlast/shared": "workspace:*"
+    "@atlast/shared": "workspace:*",
+    "webextension-polyfill": "^0.12.0"
   },
   "devDependencies": {
     "@types/chrome": "^0.0.256",
+    "@types/webextension-polyfill": "^0.12.4",
     "autoprefixer": "^10.4.23",
     "cssnano": "^7.1.2",
     "esbuild": "^0.19.11",

packages/extension/src/background/service-worker.ts

···
+import browser from 'webextension-polyfill';
 import {
   MessageType,
   onMessage,
···
 /**
  * Log extension installation
  */
-chrome.runtime.onInstalled.addListener((details) => {
+browser.runtime.onInstalled.addListener((details) => {
   console.log('[Background] Extension installed:', details.reason);
 
   if (details.reason === 'install') {

packages/extension/src/lib/api-client.ts

···
  * ATlast API client for extension
  */
 
+import browser from 'webextension-polyfill';
+
 // These are replaced at build time by esbuild
 declare const __ATLAST_API_URL__: string;
 declare const __BUILD_MODE__: string;
···
  * Get extension version from manifest
  */
 export function getExtensionVersion(): string {
-  return chrome.runtime.getManifest().version;
+  return browser.runtime.getManifest().version;
 }
 
 /**

packages/extension/src/lib/messaging.ts

···
+import browser from 'webextension-polyfill';
 import type { ScraperProgress, ScraperResult } from '../content/scrapers/base-scraper.js';
 
 /**
···
  * Send message to background script
  */
 export function sendToBackground<T = any>(message: Message): Promise<T> {
-  return chrome.runtime.sendMessage(message);
+  return browser.runtime.sendMessage(message);
 }
 
 /**
  * Send message to active tab's content script
  */
 export async function sendToContent(message: Message): Promise<any> {
-  const [tab] = await chrome.tabs.query({ active: true, currentWindow: true });
+  const [tab] = await browser.tabs.query({ active: true, currentWindow: true });
   if (!tab.id) {
     throw new Error('No active tab found');
   }
-  return chrome.tabs.sendMessage(tab.id, message);
+  return browser.tabs.sendMessage(tab.id, message);
 }
 
 /**
  * Listen for messages
  */
 export function onMessage(
-  handler: (message: Message, sender: chrome.runtime.MessageSender) => any | Promise<any>
+  handler: (message: Message, sender: browser.Runtime.MessageSender) => any | Promise<any>
 ): void {
-  chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
+  browser.runtime.onMessage.addListener((message, sender, sendResponse) => {
     const result = handler(message, sender);
 
     // Handle async handlers

packages/extension/src/lib/storage.ts

···
+import browser from 'webextension-polyfill';
 import type { ExtensionState } from './messaging.js';
 
 /**
···
  * Get extension state from storage
  */
 export async function getState(): Promise<ExtensionState> {
-  const result = await chrome.storage.local.get(STORAGE_KEYS.STATE);
+  const result = await browser.storage.local.get(STORAGE_KEYS.STATE);
   return result[STORAGE_KEYS.STATE] || { status: 'idle' };
 }
 
···
  * Save extension state to storage
  */
 export async function setState(state: ExtensionState): Promise<void> {
-  await chrome.storage.local.set({ [STORAGE_KEYS.STATE]: state });
+  await browser.storage.local.set({ [STORAGE_KEYS.STATE]: state });
 }
 
 /**
  * Clear extension state
  */
 export async function clearState(): Promise<void> {
-  await chrome.storage.local.remove(STORAGE_KEYS.STATE);
+  await browser.storage.local.remove(STORAGE_KEYS.STATE);
 }

packages/extension/src/popup/popup.ts

···
+import browser from 'webextension-polyfill';
 import {
   MessageType,
   sendToBackground,
···
     // Open ATlast at results page with upload data
     const { getApiUrl } = await import('../lib/api-client.js');
     const resultsUrl = `${getApiUrl()}${response.redirectUrl}`;
-    chrome.tabs.create({ url: resultsUrl });
+    browser.tabs.create({ url: resultsUrl });
 
   } catch (error) {
     console.error('[Popup] Error uploading:', error);
···
 
     // Set up login buttons
     elements.btnOpenAtlast.addEventListener('click', () => {
-      chrome.tabs.create({ url: getApiUrl() });
+      browser.tabs.create({ url: getApiUrl() });
     });
 
     elements.btnRetryLogin.addEventListener('click', async () => {
···
   });
 
   // Listen for storage changes (when background updates state)
-  chrome.storage.onChanged.addListener((changes, areaName) => {
+  browser.storage.onChanged.addListener((changes, areaName) => {
     if (areaName === 'local' && changes.extensionState) {
       const newState = changes.extensionState.newValue;
       console.log('[Popup] 🔄 Storage changed, new state:', newState);