Firefox

uBlock Origin – Efficient general-purpose ad blocker.
privacytools.io – Guide to enhancing the privacy of Firefox.
- Smart Referer – for the sites that break due to XOriginTrimming

Dark Reader – Give almost every site a dark mode.
Foxy Gestures – Because I used Opera just long enough (a long time ago) to get used to mouse gestures.
Amazon SMILE! – Automatically redirect Amazon to Amazon Smile so I can donate to charity without all the bloat of the Amazon Assitant extension.
Kee – Because KeePass is the best FOSS password manager.
Enhancer for YouTube™ – Lots of experience improvements on YouTube.
Stylus – Stylesheet injection when Dark Reader doesn’t cut it.

Search engine: DuckDuckGo – Check out all these shortcuts, and extra privacy as well.
Theme: Dark by Mozilla
Disable fade transition to full screen: in about:config, set full-screen-api.transition-duration.enter and full-screen-api.transition-duration.enter to 0 0