Firebase: Why I am getting service worker registration error

I am trying to implement push messaging using firebase. For this, I have followed google doc as well as script that google shared on github. You can find the same on below URL:

Firebase Push Messaging Source Code

And also followed below tutorials:

JS Setup from Google Tutorial

How to Setup Push Messaging on Localhost

Below is my folder structure:

root
 |--push-demo
 |     |
 |     |--index.html
 |     |--index.js
 |
 |--firebase-messaging-sw.js

I have followed everything that describes in all the above links. As per requirement, I have also done following things:

1. Enable SSL on localhost
2. Put firebase-messaging-sw.js in root folder
3. Path for all the included JS files are correct. I mean when I open them in browser, browser is showing me JS content.
4. Generated VAPID key from firebase console and used the same.
5. Also enable allow-insecure-localhost in chrome

After doing everything correctly, I am getting below error:

FirebaseError: Messaging: We are unable to register the default service worker. Failed to register a ServiceWorker for scope ('https://localhost/firebase-cloud-messaging-push-scope') with script ('https://localhost/firebase-messaging-sw.js'): An SSL certificate error occurred when fetching the script. (messaging/failed-service-worker-registration).

Can someone please guide me about what is wrong at my side? I have looked many solutions on forums, and everyone is saying about either enable SSL on localhost or put your service file in root folder. But still I am getting error.

Thanks in advance.