1. Introduction

In this tutorial, we will learn how to identify performance bottlenecks in a web application using Firebase Performance Monitoring and then fix them to optimize the app's performance.

By the end, you will:
1. Understand what performance bottlenecks are.
2. Know how to use Firebase Performance Monitoring to identify bottlenecks.
3. Be able to fix common performance issues.

Prerequisites:
- Basic understanding of JavaScript and web development.
- Familiarity with Firebase (though we will cover the basics).

2. Step-by-Step Guide

2.1 What are Performance Bottlenecks?

Performance bottlenecks occur when a part of your application restricts its overall speed, causing the app to slow down or fail to scale. Identifying and resolving these bottlenecks can significantly improve your app's performance.

2.2 Using Firebase Performance Monitoring

Firebase Performance Monitoring is a tool that helps you gain insights into the performance characteristics of your app. It can automatically measure app startup time, HTTP/S network requests, and provides an API for custom tracing.

To set up Firebase Performance Monitoring, you need to:

1. Install the Firebase SDK in your application.
2. Initialize Firebase Performance Monitoring.
3. Start using the tool.

2.3 Fixing Performance Bottlenecks

Once you've identified the bottlenecks, the next step is to fix them. This could involve optimizing your code, reducing network calls, splitting heavy tasks into smaller ones, etc.

3. Code Examples

3.1 Installing Firebase SDK

// Using npm
npm install --save firebase

// Using yarn
yarn add firebase

3.2 Initializing Firebase Performance Monitoring

// Import firebase
import * as firebase from 'firebase/app';

// Add the Performance Monitoring library
import 'firebase/performance';

// Initialize Firebase
const firebaseConfig = {
  // your config here
};
firebase.initializeApp(firebaseConfig);

// Initialize Performance Monitoring
const perf = firebase.performance();

3.3 Using Firebase Performance Monitoring

// Start a custom trace
var trace = perf.trace('customTraceName');
trace.start();

// Your code here

// Stop the trace
trace.stop();

4. Summary

We've learned what performance bottlenecks are, how to identify them using Firebase Performance Monitoring, and how to start addressing them.

For further learning, explore more about Firebase Performance Monitoring, ways to optimize JavaScript code, and strategies to reduce network latency.

5. Practice Exercises

1. Exercise 1: Set up Firebase Performance Monitoring in a sample web app.

2. Solution: Follow the steps outlined in this tutorial. Remember to replace the Firebase config with your own.

3. Exercise 2: Identify a performance bottleneck using Firebase Performance Monitoring.

4. Solution: Create a custom trace around a piece of code that you suspect might be causing a performance issue. Analyze the trace data in the Firebase console.

5. Exercise 3: Fix the identified performance bottleneck.

6. Solution: This will depend on what the bottleneck is. Some general tips include optimizing your code, reducing the number of network calls, and splitting heavy tasks into smaller ones.

Keep practicing by identifying and fixing more performance bottlenecks in your app!