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Updated on GitHub 4 months ago (see history)

How to configure Firefox for privacy and security

Firefox privacy and security hardening guide (2022 revised edition)


  • When copy/pasting commands that start with $, strip out $ as this character is not part of the command

Setup guide

Step 1: install Firefox

Go to, download and install Firefox.

Step 2: add user.js to profile

Heads-up: enables Mullvad DNS over HTTPS.

Heads-up: see arkenfox/user.js to explore more settings.

Start Firefox, paste “about:profiles” in address bar and press enter.

Find default profile root directory and copy to clipboard.

Download user.js to default profile root directory.

Heads-up: replace /Users/sunknudsen/Library/Application Support/Firefox/Profiles/rzrw17yo.default-release with default profile root directory copied to clipboard.

$ cd "/Users/sunknudsen/Library/Application Support/Firefox/Profiles/rzrw17yo.default-release"
$ curl --fail --remote-name

Step 3: restart Firefox

Step 4: install Firefox Multi-Account Containers and Privacy Badger extensions

Go to and click “Add to Firefox”.

Go to and click “Add to Firefox”.

Heads-up: when asked to allow extension to run in private windows, check box and click “Okay”.

Step 5: set default search engine to DuckDuckGo

Step 6: configure containers (see episode)

Step 7: check for DNS and WebRTC leaks

Go to

Connection check

No DNS leaks

No WebRTC leaks


Usage guide

Temporarily disable cookie and site data deletion (useful when Firefox is restarted to install update or one wishes to reboot computer while persisting Firefox sessions)

Heads-up: “Delete cookies and site data when Firefox is closed” will be enabled again next time Firefox starts.

Start Firefox, paste “about:preferences#privacy” in address bar and press enter.

Disable “Delete cookies and site data when Firefox is closed”.


Want things back the way they were before following this guide? No problem!

Delete user.js and set Firefox settings as they were before following guide.


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