diff --git a/extension/lib/api.js b/extension/lib/api.js
new file mode 100644
index 0000000..60fc95d
--- /dev/null
+++ b/extension/lib/api.js
@@ -0,0 +1,93 @@
+/**
+ * FC backend client. Talks to /api/credentials (FC-3b), /api/sources
+ * (FC-3a), and the new /api/extension/* endpoints (FC-3g).
+ */
+
+class FabledCuratorAPI {
+  constructor() {
+    this.baseUrl = null;
+    this.apiKey = null;
+  }
+
+  async init() {
+    const cfg = await browser.storage.local.get(['apiUrl', 'apiKey']);
+    this.baseUrl = cfg.apiUrl || null;
+    this.apiKey = cfg.apiKey || null;
+    return this.isConfigured();
+  }
+
+  isConfigured() {
+    return !!(this.baseUrl && this.apiKey);
+  }
+
+  async request(method, endpoint, data = null) {
+    if (!this.isConfigured()) {
+      throw new Error('Not configured. Set FC URL + API key in settings.');
+    }
+    const url = `${this.baseUrl.replace(/\/+$/, '')}${endpoint}`;
+    const options = {
+      method,
+      headers: {
+        'Content-Type': 'application/json',
+        'X-Extension-Key': this.apiKey,
+      },
+    };
+    if (data) options.body = JSON.stringify(data);
+
+    let response;
+    try {
+      response = await fetch(url, options);
+    } catch (e) {
+      throw new Error('Cannot connect to FabledCurator. Check URL.');
+    }
+
+    if (!response.ok) {
+      let message;
+      try {
+        const body = await response.json();
+        message = body.error || `HTTP ${response.status}`;
+        if (body.detail) message += `: ${body.detail}`;
+      } catch {
+        message = `HTTP ${response.status}: ${response.statusText}`;
+      }
+      const err = new Error(message);
+      err.status = response.status;
+      throw err;
+    }
+
+    if (response.status === 204) return { success: true };
+    return response.json();
+  }
+
+  // FC-3b — credentials.
+  uploadCredentials(platform, credentialType, data) {
+    return this.request('POST', '/credentials', {
+      platform,
+      credential_type: credentialType,
+      data,
+    });
+  }
+  getCredentials() {
+    return this.request('GET', '/credentials');
+  }
+
+  // FC-3a — sources.
+  listSources() {
+    return this.request('GET', '/sources');
+  }
+  triggerSourceCheck(sourceId) {
+    return this.request('POST', `/sources/${sourceId}/check`);
+  }
+
+  // FC-3g — extension-specific.
+  quickAddSource(url) {
+    return this.request('POST', '/extension/quick-add-source', { url });
+  }
+
+  // Connection test = the cheapest read with auth.
+  testConnection() {
+    return this.request('GET', '/credentials');
+  }
+}
+
+const api = new FabledCuratorAPI();
diff --git a/extension/lib/cookies.js b/extension/lib/cookies.js
new file mode 100644
index 0000000..b13ca4d
--- /dev/null
+++ b/extension/lib/cookies.js
@@ -0,0 +1,56 @@
+/**
+ * Cookie extraction + Netscape format conversion.
+ * Direct port of GS extension/lib/cookies.js.
+ */
+
+async function extractCookiesForPlatform(platformKey) {
+  const platform = PLATFORMS[platformKey];
+  if (!platform) throw new Error(`Unknown platform: ${platformKey}`);
+
+  const all = [];
+  for (const domain of platform.domains) {
+    try {
+      const cookies = await browser.cookies.getAll({ domain });
+      all.push(...cookies);
+    } catch (e) {
+      console.warn(`cookies.getAll failed for ${domain}:`, e);
+    }
+  }
+  return deduplicateCookies(all);
+}
+
+function deduplicateCookies(cookies) {
+  const seen = new Map();
+  for (const c of cookies) {
+    const key = `${c.name}|${c.domain}|${c.path}`;
+    if (!seen.has(key)) {
+      seen.set(key, c);
+    } else {
+      const existing = seen.get(key);
+      if (c.expirationDate && (!existing.expirationDate || c.expirationDate > existing.expirationDate)) {
+        seen.set(key, c);
+      }
+    }
+  }
+  return Array.from(seen.values());
+}
+
+function toNetscapeFormat(cookies) {
+  const lines = ['# Netscape HTTP Cookie File'];
+  for (const c of cookies) {
+    let domain = c.domain.replace(/^\.?www\./, '.');
+    if (!domain.startsWith('.')) domain = '.' + domain;
+    const secure = c.secure ? 'TRUE' : 'FALSE';
+    const expiration = c.expirationDate ? Math.floor(c.expirationDate) : 0;
+    lines.push([domain, 'TRUE', c.path || '/', secure, String(expiration), c.name, c.value].join('\t'));
+  }
+  return lines.join('\n');
+}
+
+async function getCookieCount(platformKey) {
+  try {
+    return (await extractCookiesForPlatform(platformKey)).length;
+  } catch {
+    return 0;
+  }
+}