Here are two pages to visit to safeguard your privacy when using Firefox. Please BE CAREFUL when making changes such as these; you probably do not want to make every single change shown because if you do, you may experience unintended consequences, and may possibly even “break” certain web sites:
1. Firefox Privacy – The Complete How-To Guide
Mozilla Firefox is arguably the best browser available that combines strong privacy protection features, good security, active development, and regular updates. The newest version of Firefox is fast, light-weight, and packed full of great settings to protect your privacy.
It is for this reason that I consider Firefox to be the best all-around browser for privacy and security. It remains a solid alternative to some of the other options, such as Google Chrome, Microsoft Edge, and Safari.
Another great aspect of Firefox is that it is highly customizable, which is the point of this guide. Below we will go over how you can customize Firefox to give you the security and privacy you desire, while still working well for day-to-day browsing.
Source: Firefox Privacy – The Complete How-To Guide (Restore Privacy)
2. Privacy/Privacy Task Force/firefox about config privacy tweeks
Firefox: Privacy Related “about:config” Tweaks
This is a collection of privacy related about:config tweaks. We’ll show you how to enhance the privacy of your Firefox browser.
Source: Privacy/Privacy Task Force/firefox about config privacy tweeks (Mozilla Wiki)