import { initializeApp } from 'firebase/app';
import { getFirestore } from 'firebase/firestore';
import { Capacitor } from '@capacitor/core';
import { initializeAuth, indexedDBLocalPersistence } from 'firebase/auth';
import { getAuth } from 'firebase/auth';

const firebaseApp = initializeApp({
 apiKey: process.env.VUE_APP_FIREBASE_API_KEY,
 authDomain: process.env.VUE_APP_FIREBASE_AUTH_DOMAIN,
 databaseURL: process.env.VUE_APP_FIREBASE_DATABASE_URL,
 projectId: process.env.VUE_APP_FIREBASE_PROJECT_ID,
 storageBucket: process.env.VUE_APP_FIREBASE_STORAGE_BUCKET,
 messagingSenderId: 
 process.env.VUE_APP_FIREBASE_MESSAGING_SENDER_ID,
 appId: process.env.VUE_APP_FIREBASE_APP_ID,
});


function whichAuth() {
  let auth
  if (Capacitor.isNativePlatform()) {
    auth = initializeAuth(firebaseApp, {
      persistence: indexedDBLocalPersistence
    })
  } else {
    auth = getAuth()
  }
  return auth
}

export const auth = whichAuth()
const db = getFirestore();

export const auth = whichAuth();
export { firebaseApp, db };

Then in your component, cal your method like this await signInAnonymously(auth);. Don't forget to import the auth we exported at the top.

Been struggling a lot with this issue too but I managed to fix it. For those who need help here's my code.

You can delete all Firebase related imports from app.module.ts since this solution only uses Firebase. The packages rxfire and @angular/fire can be removed from your package.json. The only dependency I have is "firebase": "^9.6.1". I used observables for the getObject and list functions since that's what I'm used to and I didn't want to rewrite my original code.

import { Injectable } from '@angular/core';
import { Capacitor } from '@capacitor/core';
import { environment } from '@environment';
import { initializeApp } from 'firebase/app';
import { Auth, getAuth, indexedDBLocalPersistence, initializeAuth, signInWithCustomToken } from 'firebase/auth';
import { Database, getDatabase, onValue, orderByChild, query, ref } from 'firebase/database';
import { Observable, Observer, from } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class FirebaseService {
  private readonly database: Database;
  private readonly auth: Auth;

  constructor() {
    const firebaseApp = initializeApp(environment.firebase);

    if (Capacitor.isNativePlatform()) {
      initializeAuth(firebaseApp, {
        persistence: indexedDBLocalPersistence
      });
    }

    this.database = getDatabase(firebaseApp);
    this.auth = getAuth(firebaseApp);
  }

  connectFirebase(firebaseToken) {
    return from(signInWithCustomToken(this.auth, firebaseToken));
  }

  disconnectFirebase() {
    return from(this.auth.signOut());
  }

  getObject<T>(path: string): Observable<T> {
    return new Observable((observer: Observer<T>) => {
      const dbRef = ref(this.database, path);
      const listener = onValue(dbRef, snapshot => {
        const data = snapshot.val();
        observer.next(data);
      });

      return {
        unsubscribe() {
          listener();
        }
      };
    });
  }

  public list<T>(path: string, orderChildBy?: string): Observable<Array<T>> {
    return new Observable<Array<T>>((observer: Observer<Array<T>>) => {
      const dbRef = ref(this.database, path);
      const dbReference = !orderChildBy ? dbRef : query(dbRef, orderByChild(orderChildBy));

      const listener = onValue(dbReference, snapshot => {
        const data = Object.values<T>(snapshot.val() || {});
        console.log(path, data);
        observer.next(data);
      });

      return {
        unsubscribe() {
          listener();
        }
      };
    });
  }
}

For those who can't see the error message thrown by firebase try the following command in your Safari console to see the error.

window.location.reload()

The real problem: firebase-js-sdk on mobile iOS assumes google API (gapi) exists on the window, even when it isn't used.

I found a work around: Mock window.gapi before using firebase auth login:

window['gapi'] = {
  load: (name: string) => Promise.resolve(),
  iframes: {
    getContext: () => {
      return {
        iframe: {
          contentWindow: {
            postMessage: (message: any) => {
              console.log("gapi iframe message:", message);
            }
          }
        }
      }
    }
  }
} as any;