Firefox

Extensions

GitHub uMatrix filters net requests.

GitHub uBlocko is a general-purpose blocker.

GitHub CanvasBlocker blocks canvas-API to prevent canvas fingerprinting.

GitLab Decentraleyes - local emulation of Content Delivery Networks (CDN).

AMO Don't track me Google removes the annoying link-conversion at Google Search / maps / ... GitHub Source

AMO Bookmark search plus 2 displays and filters bookmarks on search string, show parent folders GitHub Source

AMO Print Edit WE helps to choose the contents of a web page prior to printing.

AMO Dark Mode is a dark theme for the web.

AMO Markdown Viewer Webext is Markdown (.md) file viewer. GitHub Source, Note for Linux users

AMO Fennec TextWrap adds textwrap to Firefox on Android. GitHub Source

AMO ClearURLs removes the tracking fields from URLs. GitLab Source

Configuration

The large number of browser settings can be configured via user.js. Create your user.js somewhere and drop it into your Profile directory.

Comprehensive user.js template for configuring and hardening Firefox - ghacksuserjs

user.js - Firefox configuration hardening - pyllyukko

Descriptions of some Firefox settings - DonQuixoteI

Firefox Configuration Guide for Privacy Freaks and Performance Buffs - 12bytes.org

Privacy-Handbuch - privacy-handbuch.de (in German)

Firefox Tuning zur Absicherung und Anonymisierung - kairaven.de (in German)

A brief guide to Mozilla preferences - MDN

Locking preferences - MozillaZine

Release/Build/Source

Firefox Releases: Desktop, Mobile

Release Calendar

Mercurial/releases/mozilla-beta/tags

Nightly Firefox source code search tool (DXR)

Forums

mozillaZine Forums

Firefox Builds - mozillaZine Forums