From LetsWriteCode:
https://www.youtube.com/watch?app=desktop&v=Ipa58NVGs_c
https://github.com/shama/letswritecode/blob/master/how-to-make-chrome-extensions/bear/content.js
This video and hence code takes you through how you can:
- run chrome extensions locally,
- how to access the DOM of all open tabs in the window
- how to make small popup windows when the chrome extension icon
- how to create a new tab and populate content on it
I would fully recommend!