diff --git a/extension/lib/api.js b/extension/lib/api.js
index a6b71b2..e66ea93 100644
--- a/extension/lib/api.js
+++ b/extension/lib/api.js
@@ -11,7 +11,10 @@ class FabledCuratorAPI {
 
   async init() {
     const cfg = await browser.storage.local.get(['apiUrl', 'apiKey']);
-    this.baseUrl = cfg.apiUrl || null;
+    // Normalize on READ, not just on save: configs stored before the options
+    // page started normalizing are missing the `/api` suffix, and this heals
+    // them without the operator having to reopen Settings.
+    this.baseUrl = normalizeApiUrl(cfg.apiUrl) || null;
     this.apiKey = cfg.apiKey || null;
     return this.isConfigured();
   }
@@ -50,6 +53,13 @@ class FabledCuratorAPI {
       } catch {
         message = `HTTP ${response.status}: ${response.statusText}`;
       }
+      // 404/405 from FC almost always means the request never reached the JSON
+      // API — it fell through to the SPA catch-all, which serves HTML on GET
+      // and rejects everything else. Say so, rather than making the operator
+      // decode "Method Not Allowed" on an endpoint that plainly allows POST.
+      if (response.status === 404 || response.status === 405) {
+        message += ` — ${url} isn't the FC API. Check the FC URL in settings.`;
+      }
       const err = new Error(message);
       err.status = response.status;
       throw err;
@@ -96,11 +106,10 @@ class FabledCuratorAPI {
     return this.request('GET', '/extension/manifest');
   }
 
-  // The web/SPA root: baseUrl with the trailing slash + `/api` suffix stripped.
-  // Where the Vue router (artist pages) and the served XPI live, NOT the JSON
-  // API. Used by OPEN_ARTIST_PAGE + the self-update check.
+  // The web/SPA root: where the Vue router (artist pages) and the served XPI
+  // live, NOT the JSON API. Used by OPEN_ARTIST_PAGE + the self-update check.
   webRoot() {
-    return (this.baseUrl || '').replace(/\/+$/, '').replace(/\/api$/, '');
+    return webRootFromApiUrl(this.baseUrl);
   }
 
   // Connection test = the cheapest read with auth.
diff --git a/extension/lib/url.js b/extension/lib/url.js
new file mode 100644
index 0000000..2329adf
--- /dev/null
+++ b/extension/lib/url.js
@@ -0,0 +1,32 @@
+/**
+ * Canonical FC endpoint derivation, shared by the background client and the
+ * options page so a URL entered either way behaves identically.
+ *
+ * FC serves two things on one origin: the JSON API under `/api`, and the Vue
+ * SPA from the root. `api.js` builds requests as `${baseUrl}/credentials`, so
+ * the stored base URL has to carry the `/api` suffix.
+ */
+
+/**
+ * Accept what an operator would naturally type — the instance root
+ * (`http://curator.example.com`) or the API root (`.../api`) — and return the
+ * API root either way.
+ *
+ * Worth normalizing rather than validating: a root-form URL doesn't fail
+ * loudly, it lands on the SPA catch-all, which answers `GET /credentials` with
+ * 200 HTML and rejects `POST /credentials` with 405. The operator sees a
+ * working Test Connection and a broken export.
+ */
+function normalizeApiUrl(raw) {
+  const trimmed = (raw || '').trim().replace(/\/+$/, '');
+  if (!trimmed) return '';
+  return /\/api$/i.test(trimmed) ? trimmed : `${trimmed}/api`;
+}
+
+/**
+ * The SPA root — where the Vue router (artist pages) and the served XPI live,
+ * NOT the JSON API. Accepts either input form, same as normalizeApiUrl.
+ */
+function webRootFromApiUrl(raw) {
+  return normalizeApiUrl(raw).replace(/\/api$/i, '');
+}
diff --git a/extension/manifest.json b/extension/manifest.json
index 4348ba1..e763e3f 100644
--- a/extension/manifest.json
+++ b/extension/manifest.json
@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "FabledCurator",
-  "version": "1.0.9",
+  "version": "1.0.10",
   "description": "Export cookies from supported platforms to FabledCurator and add creators as sources in one click.",
 
   "browser_specific_settings": {
@@ -46,7 +46,7 @@
   },
 
   "background": {
-    "scripts": ["lib/platforms.js", "lib/cookies.js", "lib/api.js", "background/background.js"]
+    "scripts": ["lib/platforms.js", "lib/cookies.js", "lib/url.js", "lib/api.js", "background/background.js"]
   },
 
   "options_ui": {
diff --git a/extension/options/options.html b/extension/options/options.html
index 27e5136..9af858c 100644
--- a/extension/options/options.html
+++ b/extension/options/options.html
@@ -21,9 +21,12 @@
 <body>
   <h1>FabledCurator extension</h1>
 
-  <label for="api-url">FC base URL</label>
-  <input id="api-url" type="url" placeholder="http://curator.example.com/api" />
-  <div class="hint">Find this on FC → Settings → Maintenance → Browser extension.</div>
+  <label for="api-url">FC instance URL</label>
+  <input id="api-url" type="url" placeholder="http://curator.example.com" />
+  <div class="hint">
+    Your FabledCurator address — with or without the trailing <code>/api</code>; both work.
+    Find it on FC → Settings → Maintenance → Browser extension.
+  </div>
 
   <label for="api-key">Extension API key</label>
   <input id="api-key" type="password" placeholder="paste from FC Settings card" />
@@ -36,6 +39,7 @@
 
   <div id="status" class="status" style="display:none;"></div>
 
+  <script src="../lib/url.js"></script>
   <script src="options.js"></script>
 </body>
 </html>
diff --git a/extension/options/options.js b/extension/options/options.js
index 4798183..e453273 100644
--- a/extension/options/options.js
+++ b/extension/options/options.js
@@ -8,7 +8,7 @@ document.addEventListener('DOMContentLoaded', async () => {
 });
 
 async function save() {
-  const apiUrl = document.getElementById('api-url').value.trim().replace(/\/+$/, '');
+  const apiUrl = normalizeApiUrl(document.getElementById('api-url').value);
   const apiKey = document.getElementById('api-key').value.trim();
   if (!apiUrl || !apiKey) {
     showStatus('Both fields are required.', 'err');
@@ -16,11 +16,14 @@ async function save() {
   }
   await browser.storage.local.set({ apiUrl, apiKey });
   await browser.storage.local.remove(['lastConnectionTest', 'lastConnectionStatus']);
-  showStatus('Saved.', 'ok');
+  // Show what was actually stored — the operator may have typed the instance
+  // root and it was normalized to the API root.
+  document.getElementById('api-url').value = apiUrl;
+  showStatus(`Saved — using ${apiUrl}`, 'ok');
 }
 
 async function test() {
-  const apiUrl = document.getElementById('api-url').value.trim().replace(/\/+$/, '');
+  const apiUrl = normalizeApiUrl(document.getElementById('api-url').value);
   const apiKey = document.getElementById('api-key').value.trim();
   if (!apiUrl || !apiKey) {
     showStatus('Fill both fields first.', 'err');
@@ -31,8 +34,23 @@ async function test() {
       method: 'GET',
       headers: { 'X-Extension-Key': apiKey },
     });
-    if (r.ok) showStatus(`Connected — HTTP ${r.status}.`, 'ok');
-    else showStatus(`HTTP ${r.status}: ${r.statusText}`, 'err');
+    if (!r.ok) {
+      showStatus(`HTTP ${r.status}: ${r.statusText}`, 'err');
+      return;
+    }
+    // A 200 is NOT sufficient. If the URL resolves to the Vue SPA instead of
+    // the JSON API, the catch-all route returns 200 with an HTML document —
+    // which used to report "Connected" on a config that could not POST at all.
+    const contentType = r.headers.get('content-type') || '';
+    if (!contentType.includes('json')) {
+      showStatus(
+        `${apiUrl} answered with ${contentType || 'no content-type'}, not JSON `
+          + '— that looks like the FC web UI rather than its API.',
+        'err',
+      );
+      return;
+    }
+    showStatus(`Connected to ${apiUrl} — HTTP ${r.status}.`, 'ok');
   } catch (e) {
     showStatus(`Cannot reach ${apiUrl}: ${e.message}`, 'err');
   }
diff --git a/extension/package.json b/extension/package.json
index 16a9858..8230440 100644
--- a/extension/package.json
+++ b/extension/package.json
@@ -1,6 +1,6 @@
 {
   "name": "fabledcurator-extension",
-  "version": "1.0.9",
+  "version": "1.0.10",
   "private": true,
   "description": "Firefox extension for FabledCurator",
   "scripts": {