`goto({ waitUntil: "hydration" })` times out on Firefox — `window.useNuxtApp?.().isHydrating` never resolves

[jeffjenx]

Environment

• Operating System: Windows 11 Enterprise (10.0.26100)
• Node Version: v20.20.0
• Nuxt Version: 4.4.2
• CLI Version: 3.34.0
• Nitro Version: 2.13.3
• Package Manager: npm@11.10.1
• Builder: vite
• @nuxt/test-utils Version: 4.0.0
• @playwright/test Version: 1.59.1
• Vue Version: 3.5.32

Reproduction

Minimal repro using the test-utils example app:

1. Clone the https://stackblitz.com/github/nuxt/test-utils/tree/main/examples/app-vitest or any Nuxt app with Playwright E2E tests
2. Add a Firefox project to playwright.config.ts:

projects: [
  { name: "chromium", use: { ...devices["Desktop Chrome"] } },
  { name: "firefox", use: { ...devices["Desktop Firefox"] } },
]

3. Write a test using goto with waitUntil: "hydration":

import { expect, test } from "@nuxt/test-utils/playwright";

test("page loads", async ({ page, goto }) => {
  await goto("/", { waitUntil: "hydration" });
  await expect(page.locator("body")).toBeVisible();
});

4. Run: npx playwright test
5. Chromium passes. Firefox times out at goto().

Describe the bug

When using goto(url, { waitUntil: "hydration" }) with Playwright's Firefox project, the call never resolves and the test times out. The page loads fully — Playwright's page snapshot confirms the entire DOM is rendered, auth works, routing completes — but the hydration detection never fires.

The root cause is in https://github.com/nuxt/test-utils/blob/main/src/e2e/browser.ts#L69:

await page.waitForFunction(() => window.useNuxtApp?.().isHydrating === false)

In Firefox, this waitForFunction call never resolves. Either window.useNuxtApp is not exposed to the page's global scope in Firefox, or isHydrating never transitions from true to false.

This affects 100% of tests that use waitUntil: "hydration" (or waitUntil: "route"), making Firefox E2E testing impossible with @nuxt/test-utils.

Chromium: passes
WebKit: passes
Firefox: 0% pass rate (all timeout)

Additional context

• The app renders and functions correctly in Firefox — this is purely a test-utils detection issue, not a browser compatibility problem.
• Tested with a production Nuxt 4.4.2 app (55 E2E specs). Chromium and WebKit both pass 100%. Firefox fails 100%, all at the waitForHydration call.
• The waitUntil: "route" option (line 72, same file) likely has the same issue since it also relies on window.useNuxtApp?.().
• Playwright version 1.59.1 with Firefox 148.0.2.

Logs

Error: page.goto: Test timeout of 30000ms exceeded.

Call log:
  - navigating to "https://example.com/", waiting until "load"
    at goto (node_modules/@nuxt/test-utils/dist/playwright.mjs:46:35)