Hi, here are the extensions I use in FireFox/Librewolf (all will work in Chromium too, but I don't recommend Chromium browsers):
Privacy and Security-focused
uBlock Origin: A lightweight and efficient wide-spectrum content blocker.
Decentraleyes: Protects you from tracking through free, centralized content delivery. (not recommended alongside uBlock Origin; see the reply below)
CanvasBlocker: Protects your privacy by preventing websites from fingerprinting you using the Canvas API.
Ghostery Tracker & Ad Blocker - Privacy AdBlock: Blocks trackers and ads to protect your privacy and speed up browsing. Also has a handy feature that automatically rejects cookies for you. (not recommended alongside uBlock Origin; see the reply below. You can disable the ad blocking functionality and keep the cookie rejection function).
KeePassXC-Browser: Integrates KeePassXC password manager with your browser.
NoScript: Blocks JavaScript, Flash, and other executable content to protect against XSS and other web-based attacks (note: you will be required to manually activate javascript on each web page that you visit, but this is a good practice that you should get used to).
Privacy Badger: Automatically learns to block trackers based on their behavior. (not recommended alongside uBlock Origin; see the reply below)
User-Agent Switcher and Manager: Allows you to spoof your browser’s user-agent string (avoid creating a unique configuration; opt for something common, such as Chrome on Windows 10).
Violentmonkey: A user script manager for running custom scripts on websites (allows you to execute your own JavaScript code, usually to modify how a website behaves or block behavior that you don't like. VERY useful. Check out greasyfork for UserScripts).
Other useful extensions (non-privacy/security)
Firefox Translations: Provides on-demand translation of web pages directly within Firefox.
Flagfox: Displays a flag depicting the location of the current website’s server.
xBrowserSync: Syncs your browser data (bookmarks, passwords, etc.) across devices with end-to-end encryption.
Plasma Integration: Integrates Firefox with the KDE Plasma desktop environment (for linux users).
I have a novice coding question using the mouse tracking as an example: Is it possible to intercept and replace mouse tracking data with generic inputs? For example, could you implement an overlay that blocks mouse interactions, and instead of physically clicking on elements, send a direct packet to the application to simulate selecting those elements?