diff --git a/packages/functional-tests/tests/misc/l10nBundleDelivery.spec.ts b/packages/functional-tests/tests/misc/l10nBundleDelivery.spec.ts
new file mode 100644
index 00000000000..314696e81d3
--- /dev/null
+++ b/packages/functional-tests/tests/misc/l10nBundleDelivery.spec.ts
@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { expect, test } from '../../lib/fixtures/standard';
+
+// German is well translated. Avoid the EN_GB_LOCALES set, en-NZ, en-SG and
+// en-MY: AppLocalizationProvider sources those from the en-GB bundle, so they
+// would not prove delivery.
+const LOCALE = 'de';
+
+// Matches the plain path and the hashed path the static asset manifest points
+// at, for example locales/de/main.ebcab539.ftl.
+const MAIN_FTL = new RegExp(`/locales/${LOCALE}/main(\\.[0-9a-f]+)?\\.ftl$`);
+
+test.describe('severity-1', () => {
+  test.use({ locale: LOCALE });
+
+  test(`delivers the ${LOCALE} main.ftl bundle`, async ({ target, page }) => {
+    // Register the wait before navigating. A request that never happens leaves
+    // this pending, so it rejects on timeout and the test fails.
+    const ftlResponse = page.waitForResponse((response) =>
+      MAIN_FTL.test(new URL(response.url()).pathname)
+    );
+
+    const [response] = await Promise.all([
+      ftlResponse,
+      page.goto(target.contentServerUrl),
+    ]);
+
+    const context = `If ${LOCALE} was dropped from the shipping locale set, this failure is correct and the fix is the locale set, not the test.`;
+
+    expect(
+      response.status(),
+      `The ${LOCALE} main.ftl bundle did not return 200. ${context}`
+    ).toBe(200);
+
+    // Any message line proves the body is a bundle rather than an error page
+    // served with a 200. No message id is named, so l10n churn cannot fail it.
+    expect(
+      await response.text(),
+      `The ${LOCALE} main.ftl bundle did not look like FTL. ${context}`
+    ).toMatch(/^[\w-]+\s*=/m);
+  });
+});