providerRedirectStrategy returns to app but does not complete sign-in

[russellwheatley]

[REQUIRED] Describe your environment

• Operating System version: macOS
• Browser version: _
• Firebase UI version: latest
• Firebase SDK version: 11.10.0
• Package name: @firebase-oss/ui-core / @firebase-oss/ui-react

[REQUIRED] Describe the problem

When using providerRedirectStrategy(), OAuth sign-in redirects to the provider and returns to the app, but the user is not signed in afterward.
If providerRedirectStrategy() is removed/commented out, sign-in works with the default popup strategy.

Steps to reproduce

1. In the React example app, configure FirebaseUI with providerRedirectStrategy():

import { initializeUI, providerRedirectStrategy } from "@firebase-oss/ui-core";
export const ui = initializeUI({
  app: firebaseApp,
  behaviors: [
    providerRedirectStrategy(),
  ],
});

2. Run the React example app.
3. Open http://localhost:5173/screens/oauth-screen.
4. Click Google sign-in.
5. Complete the Google auth flow.
6. Browser returns to http://localhost:5173/screens/oauth-screen.

Expected: Firebase Auth completes the redirect result and the app observes a signed-in user via onAuthStateChanged.

Actual: The app returns to /screens/oauth-screen, but the user remains signed out.

Things worth checking:

• Whether getRedirectResult(ui.auth) in initializeUI() is returning null or throwing.
• Whether ui.redirectError is being set but not surfaced in the example UI.
• Whether oneTapSignIn(...) affects the redirect flow.
• Whether this depends on localhost/browser storage/authDomain redirect behavior.