Last updated: March 15, 2026

To install Arkenfox user.js, download the latest user.js file from the Arkenfox GitHub repository and place it in your Firefox profile directory (find your profile path at about:support). Use Firefox ESR for best compatibility, create a user-overrides.js file for personal exceptions, and run the included diagnostic tool to verify your configuration. This guide covers the full setup process, key privacy settings Arkenfox enforces, how it compares to alternatives, and how to troubleshoot common breakage.

What is Arkenfox user.js?

Arkenfox is a community-maintained project that provides a heavily optimized user.js file. a configuration file that overrides Firefox’s default settings. Unlike standard browser preferences, user.js entries persist across updates and can enforce settings that are otherwise hidden or reset by Mozilla.

The primary goals of Arkenfox include disabling telemetry, blocking tracking scripts, preventing fingerprinting, and removing unnecessary network requests. The configuration balances privacy with usability, though some settings may affect functionality on certain websites.

Arkenfox is not a Firefox extension or a separate browser. It is a plain text file that sits in your profile directory. Every time Firefox starts, it reads user.js and applies the settings. overriding any changes you made through the UI during the previous session. This persistence is intentional: it ensures privacy settings survive updates and accidental changes.

Prerequisites

Before implementing Arkenfox, ensure you have:

Avoid using Firefox Beta or standard Release for Arkenfox, as these channels receive updates more frequently and may reset some preferences. Firefox ESR is recommended because it receives security patches without feature churn, giving you a stable base for long-term hardening.

Step 1 - Install Arkenfox user.js

First, locate your Firefox profile directory. Open about:support in your browser and find the “Profile Directory” path. Common locations include:

Navigate to your profile folder and download the latest Arkenfox user.js from the official GitHub repository:

cd ~/Library/Application\ Support/Firefox/Profiles/YOUR-PROFILE/
curl -L -o user.js https://raw.githubusercontent.com/arkenfox/user.js/master/user.js

Alternatively, clone the entire repository for access to additional tools and version history:

git clone https://github.com/arkenfox/user.js.git arkenfox
cp arkenfox/user.js ~/Library/Application\ Support/Firefox/Profiles/YOUR-PROFILE/

Replace YOUR-PROFILE with your actual profile folder name found in about:support.

Step 2 - Understand the Configuration

Arkenfox user.js contains hundreds of settings organized by category. Key sections include:

Telemetry and Data Collection

These settings disable Mozilla’s data collection:

// Disable telemetry
user_pref("toolkit.telemetry.enabled", false);
user_pref("toolkit.telemetry.unified", false);
user_pref("datareporting.policy.dataSubmissionEnabled", false);
user_pref("datareporting.healthreport.uploadEnabled", false);

// Disable studies and experiments
user_pref("app.shield.optoutstudies.enabled", false);
user_pref("app.normandy.enabled", false);
user_pref("app.normandy.api_url", "");

Network and Connections

Arkenfox removes several Firefox “features” that make network requests without your explicit action:

// Disable captive portal detection
user_pref("network.captive-portal-service.enabled", false);
user_pref("network.connectivity-service.enabled", false);

// Disable prefetching
user_pref("network.prefetch-next", false);
user_pref("network.dns.disablePrefetch", true);
user_pref("network.predictor.enabled", false);

Disabling prefetching prevents Firefox from proactively loading pages or resolving DNS for links you hover over. While this slightly increases page load time on click, it prevents your browsing intent from being disclosed before you actually navigate.

Tracking Protection

Enhanced Tracking Protection is enforced through multiple settings:

// Enable strict tracking protection
user_pref("privacy.trackingprotection.enabled", true);
user_pref("privacy.trackingprotection.pbmode.enabled", true);
user_pref("privacy.trackingprotection.cryptomining.enabled", true);
user_pref("privacy.trackingprotection.fingerprinting.enabled", true);

Fingerprinting Resistance

Firefox includes fingerprinting countermeasures that Arkenfox enables:

// Resist fingerprinting
user_pref("privacy.resistFingerprinting", true);
user_pref("privacy.resistFingerprinting.letterboxing", true);
user_pref("webgl.disabled", true);

The privacy.resistFingerprinting setting normalizes your browser’s reported characteristics. screen resolution, timezone, fonts, canvas output. to reduce uniqueness. Letterboxing adds padding around the content area so your true window dimensions are not exposed. WebGL is disabled because it enables highly accurate fingerprinting through GPU rendering characteristics.

Cookie and Storage Isolation

Total Cookie Protection isolates cookies by site to prevent cross-site tracking:

// Enable Total Cookie Protection
user_pref("network.cookie.cookieBehavior", 5);

// Clear storage on shutdown for non-exception sites
user_pref("privacy.sanitize.sanitizeOnShutdown", true);
user_pref("privacy.clearOnShutdown.cookies", true);
user_pref("privacy.clearOnShutdown.offlineApps", true);

Setting cookieBehavior to 5 enables dFPI (dynamic First Party Isolation), the same technology that powers Total Cookie Protection. Cookies set by third-party frames are isolated per top-level site, breaking cross-site tracking without blocking third-party cookies outright.

Step 3 - Essential Customizations

While Arkenfox provides excellent defaults, you may need to adjust settings for your workflow. Create a user-overrides.js file in the same directory as user.js for personal exceptions:

Enabling Firefox Sync

If you use Firefox Sync, enable it explicitly:

// Enable sync (requires manual sign-in via Firefox UI)
user_pref("services.sync.enabled", true);

Allowing Site-Specific Exceptions

Some websites may break with strict settings. Add exceptions sparingly:

// Allow Google fonts on productivity sites
user_pref("font.minimumSize.x-western", 12);

// Whitelist specific domains from fingerprinting protection (Firefox 128+)
user_pref("privacy.resistFingerprinting.exemptedDomains", "example.com,trusted.site");

Managing WebGL

The webgl.disabled setting breaks some legitimate applications including Google Maps and certain developer tools. If you need WebGL selectively, comment out the global disable:

// user_pref("webgl.disabled", true);  // Commented out. re-enable WebGL

Consider using a browser extension like uBlock Origin to block WebGL-based fingerprinting scripts site-by-site rather than disabling WebGL globally.

Step 4 - Arkenfox vs Alternatives

Arkenfox is one of several hardening approaches for Firefox. Understanding the alternatives helps you choose the right level of hardening:

Arkenfox - Most and actively maintained Firefox hardening configuration. Requires manual setup and periodic updates. Best for power users comfortable with occasional site breakage.

Hardened Firefox guide (Privacy Guides): A curated subset of Arkenfox settings, designed for users who want strong protection with minimal breakage. Less aggressive on fingerprinting resistance.

Tor Browser - Uses privacy.resistFingerprinting and circuit-based anonymization to provide the strongest fingerprinting protection. Not based on user.js. it’s a pre-configured Firefox fork. Best when anonymity is the primary goal rather than usability.

Brave - Chromium-based browser with built-in fingerprinting protection. Easier to use but built on a different engine with different trust assumptions. Cannot use Firefox-specific privacy features like dFPI.

For most users who want strong privacy without the overhead of Tor Browser, Arkenfox with a user-overrides.js for site exceptions is the best balance.

Step 5 - Verify Your Configuration

After applying Arkenfox, verify that settings are active:

  1. Open about:config in your address bar
  2. Search for key settings like privacy.trackingprotection.enabled
  3. Confirm values match your expectations

Use the Arkenfox diagnostic tool for validation:

Run from the arkenfox repository directory
./arkenfox-gui.sh

This script checks for conflicts, missing settings, and recommends updates. Also visit coveryourtracks.eff.org to test your fingerprinting resistance and browserleaks.com to check for WebRTC and canvas leaks.

Step 6 - Updating Arkenfox

Mozilla regularly updates Firefox, which may reset or conflict with user.js settings. Use the included update script:

cd /path/to/arkenfox-repo
git pull origin master

Run the updater script (backs up old user.js and copies new one)
./updater.sh

Then re-apply your overrides
./prefsCleaner.sh

The prefsCleaner.sh script removes obsolete preferences from your profile that Arkenfox no longer manages. Run it after major Arkenfox version updates to avoid stale settings.

Troubleshooting Common Issues

Websites Not Loading

If a site fails to load, check the Browser Console (Ctrl+Shift+J) for errors. Common causes include:

Add exceptions to your user-overrides.js sparingly. Document why each exception was added so you can review them periodically.

Performance Impact

Some Arkenfox settings may slightly increase memory usage or reduce performance. The privacy.resistFingerprinting option is the most resource-intensive. If you notice slowdowns on specific sites, use the exemption mechanism:

user_pref("privacy.resistFingerprinting.exemptedDomains", "slow-site.com");

Sync Not Working

Firefox Sync requires specific settings to function. Ensure services.sync.enabled is true and sign in through the Firefox UI after each profile reset. Some Arkenfox settings disable sync-adjacent features. review the sync-related section of user.js if you rely on syncing across devices.

Frequently Asked Questions

Does Arkenfox work with Firefox for Android? Arkenfox is designed for desktop Firefox. Firefox for Android (Fenix) does not support user.js files. Use Firefox Focus or the standard Firefox Android with uBlock Origin and strict Enhanced Tracking Protection as the best alternative.

Will Arkenfox break my banking website? Banking sites commonly use scripts that conflict with fingerprinting resistance. Add your bank’s domain to privacy.resistFingerprinting.exemptedDomains in your user-overrides.js. If the site completely fails to load, try disabling privacy.resistFingerprinting temporarily in about:config to isolate the issue.

How often does Arkenfox need to be updated? Check the Arkenfox GitHub repository after major Firefox ESR updates (roughly every four months). For minor security updates, Arkenfox typically does not require changes. Subscribe to Arkenfox GitHub releases to receive notifications.

Is Arkenfox enough on its own, or do I need extensions too? Arkenfox provides excellent baseline hardening but is most effective combined with uBlock Origin (content blocking) and a DNS-over-HTTPS resolver. uBlock Origin blocks ads and trackers that slip past ETP, and DoH encrypts your DNS queries to prevent ISP-level tracking.

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