PixelBlock - Block email open tracking inside of Gmail
Facebook Clear History - Delete data that Facebook has collected on you
Ugly Email for FireFox - Get back your email privacy, block email tracking
Ghostery - Privacy tool for transparency and control
Email Privacy Protector - Check the presence of email ids on your webpages using Email Privacy Checker tool and protect yourself from email spammers.
Outline by Alphabet - Control and build your own VPN 🛠️