about:performance= Memory usage of Subprocesses.
- user.js - Firefox configuration hardening.
- Faster smarter JavaScript debugging in Firefox DevTools (2019)
- Switch from Chrome to Firefox (HN)
- webextensions-examples - Example Firefox add-ons created using the WebExtensions API.
- A Guide To New And Experimental CSS DevTools In Firefox (2019)
- Firefox Replay - Records your application, so you can track bugs down faster and understand your code better. (HN) (Explanation)
- Gecko browser engine source code
- Introduction to Firefox Debugger