Firebase is cool and all but you'll run through your free allowance fast if you choose to develop while teasting on the live servers,
because it's one accidental infinite loop away from making one too many requests.
That's why they developed firebase emulator a local testing tool which simulates firestore,authentication ,functions, storage and hosting with more features in the works .

for the detailed insatllation process
installation procedure

for the quic setup guide run

npm install -g firebase-tools

to install the firebase cli
then login by running

firebase login

then check the firebase version

firebase --version

in your projects root directory ,
start configuring by running

firebase init

In our case we need firestore ,functions and emulators , space bar to select then enter to confirm

at this point you'll need to connect your existing firebase project or create one if you don't have one

now let's set up firebase , accept the defaults

select javascript for functions and accept the defaults too and select the firestore,functions and authentication emulators

then select localhost ports for the services ,the defaults willbe good too . also select to enable the emulator UI

then allow download of the emulators
and finally strt up te emulators

firebase emulators:start

firestore also lets you import production data for firestore when you start the emulators
for that you'll need:

• the gcloud cli download

• your project needs to be on at least the blaze plan

the run

gcloud projects list

then select your project of choice project id

gcloud config set project production-c33c5

then export the data by running

gcloud firestore export gs://"your project id here".appspot.com/save        

then copy these files to your local device current directory

 gsutil -m cp -r gs://production-c33c5.appspot.com/save  .

to launch the emulator with the data run

firebase emulators:start --import ./save

you can save any changes you make by before closing the session

first run

firebase emulators:export ./save

to connect your app to the emulator
import

import { connectAuthEmulator } from "firebase/auth";
import {connectFirestoreEmulator} from "firebase/firestore"
import { connectFunctionsEmulator } from "firebase/functions";

add these to the firebaseConfig.ts at the bottom

connectFirestoreEmulator(db, 'localhost', 8080);
connectAuthEmulator(auth, "http://localhost:9099");
connectFunctionsEmulator(functions, "localhost", 5001);

another nice tip is how to run it on your lan network ,
which is helpfull if you're testing on multiple devices on the > same network.

ipconfig

and grab the ipv4 value

in the firebase.json file , change the configuration and add the host value as the ipv4 address we git from ipv4

  "emulators": {
    "firestore": {
      "port": 8080,
      "host":"192.168.43.238"

    },
    "hosting": {
      "port": 5000
    },
    "ui": {
      "enabled": true
    },
    "auth": {
      "port": 9099
    }
  }

and also in the firebaseConfig , change the connectFirebaseEmulator to:

connectFirestoreEmulator(db, '192.168.0.109', 8080);

or for auth

connectAuthEmulator(auth, "http://192.168.43.238:9099");

last thing to watch out for is port conflict , you can change the port if it's already taken or run

npx kill-port "port-number"

Happy coding