My Firefox Settings

Note: This article is imported from an old note-taking app and may be outdated.

Core Modifications & Bloatware Removal

Some guides, such as the Spyware Watchdog Mitigation Guide, recommend deleting default plugins bundled within the Firefox directory that may introduce privacy concerns or act as bloatware.

Navigate to your Firefox features directory and remove unnecessary add-ons:

cd /usr/lib/firefox/browser/features
sudo rm *.xpi

List of bundled plugins commonly removed:

firefox@getpocket.com.xpi — Pocket
followonsearch@mozilla.com.xpi — Follow-On Search
activity-stream@mozilla.org.xpi — Activity Stream
screenshots@mozilla.org.xpi — Screenshots
onboarding@mozilla.org.xpi — Onboarding
formautofill@mozilla.org.xpi — Autofill
webcompat@mozilla.org.xpi — Web Compatibility Reporter

Configuration Tweaks (about:config) (if user.js does not cover them)

Privacy, Security & Networking

accessibility.blockautorefresh: Set to true to disable forced redirections. Combining this with disabled CSS and JS yields raw, unmangled result links. (via Pedantic Software)
browser.sessionstore.interval: Set to a very high value to reduce disk writes and SessionStore tracking.

Additional Hardening Actions

Disable Firefox SessionStore: Search for browser.sessionstore in about:config and disable relevant telemetry/saving mechanisms.
Disable CSS Visited Links: Mitigates history-sniffing vulnerabilities. Read the Reddit discussion here.

User.js Templates & Generators

Instead of manually configuring about:config, you can use pre-configured user.js files.

To use a user.js file, you need to place it in your Firefox profile directory. This file is read every time Firefox starts, overriding any matching settings in about:config or prefs.js:

Navigate to about:support in your URL bar.
Find the Profile Directory row and click the Open Directory button.
Create a new text file in this directory and name it exactly user.js.
Open the file using a text editor.
Paste your desired configuration settings from the templates below into the file and save it.
Restart Firefox for the changes to take effect.

Generators:

ffprofile.com — Interactive user.js generator.
- Note on User-Agent Spoofing: While you can spoof your user-agent to a more common one (e.g., Chrome), doing so on Firefox can actually make your browser fingerprint more unique (alternative tools list). Because Firefox's engine behaves differently than Chromium, mismatched engine/user-agent data is easily detectable. For common agents, see Willhouse or WhatIsMyBrowser.

Popular Pre-configured Templates:

Arkenfox (Highly recommended, well-known)
Pyllyukko (Security focused)
Narsil's user.js (Privacy focused) (I use this one)
Vulpes
Narsil's user.js for Pale Moon (Privacy focused)
krathalan config
simeononsec FireFox Script
vermaden's Sensible Setup

Extensions & Add-ons

ximatrix: A Firefox extension similar to uMatrix capable of blocking inline scripts and advanced requests. Source code available here.
- Alternative: paraMatrix (a fork of ximatrix).
Chrome Extensions on Firefox: Firefox has introduced capabilities for importing Chrome extensions. Read the Slashdot coverage.
Extension Restrictions: Mozilla occasionally restricts add-ons on specific domains. To disable these restrictions and allow uBlock Origin to operate aggressively everywhere, read 12bytes' analysis and their uBlock suggested settings.

Browser UI & Maintenance Tweaks

Verify Database Integrity: Navigate to about:support -> Scroll down to Places Database -> Click Verify Integrity.
Turn Off Firefox Sidebar: Guide to disabling the PDF viewer sidebar.
Disable Firefox Translator: Guide to disabling built-in local translation.
Block Pop-Ups: Mozilla Support thread on native pop-up blocking.
GeckoView Config: You can access deeper settings via [chrome://geckoview/content/config.xhtml chrome://geckoview/content/config.xhtml].

Custom GUI Settings

Navigate to the standard Firefox Settings (about:preferences) to adjust the following:

General

Tabs: Enable Open links in tabs instead of new windows. Disable Show an image preview when you hover on a tab and Disable link previews.
Fonts: Uncheck Allow pages to choose their own fonts, instead of your selections above.
Language: Set to English (US). Enable Request English versions of web pages for enhanced privacy. Disable Enable full page translations.
Typing: Disable Check your spelling as you type.
Browsing & Media: Disable Enable picture-in-picture video controls and Control media via keyboard, headset, or virtual interface.

Home

New Windows and Tabs: Set both Homepage and new windows and New tabs to Blank Page.

Search

Default Search Engine: Switch to a privacy-respecting alternative like lite.duckduckgo.com, or your own self-hosted SearXNG or 4get instance.
Search Suggestions: Disable Show search suggestions.

Privacy & Security

Tracking Protection: Set Enhanced Tracking Protection to Strict (disable Fix major site issues if opting for absolute strictness without exceptions).
Global Privacy Control: Enable Tell websites not to sell or share my data.
- Note: You can also explicitly enable the Do Not Track header by setting privacy.donottrackheader.enabled to true via the hidden about:config entry.
Cookies and Site Data: Enable Delete cookies and site data when Firefox is closed.
Logins and Passwords: Disable saving passwords, payments, and addresses.
History: Set to Use custom settings for history and enable Clear history when Firefox closes.
Permissions: Disallow all requests (Location, Camera, Microphone, Notifications, etc.). Enable Block pop-up windows and Warn you when websites try to install add-ons.
Data Collection and Use: Disallow/uncheck all telemetry and data collection options.
Security: Enable HTTPS-Only Mode in all windows.
DNS over HTTPS: Set to Max Protection and select a privacy-friendly provider.

Comprehensive Hardening Guides & Reading