Firefox: Advanced Privacy Tweaks using "about:config"

Preparation:

1. Enter "about:config" in the firefox address bar and press enter.
2. Press the button "Accept the Risk and Continue"
3. Copy and paste each of the preferences below (for example "webgl.disabled") into the search bar, and set each of them to the stated value (such as "true").

Firefox Desktop:

First Party Isolation

These settings should be safe, however first party isolation may break some third party login systems.

privacy.firstparty.isolate = true

A result of the Tor Uplift effort, this preference isolates all browser identifier sources (e.g. cookies) to the first party domain, with the goal of preventing tracking across different domains. (Don't do this if you are using the Firefox Addon "Cookie AutoDelete" with Firefox v58 or below.)

Resist Fingerprinting

One of the features of resist fingerprinting is to set the reported browser timezone to UTC. If you depend on having your real time zone reported to the websites you visit, this setting may break that.

privacy.resistFingerprinting = true

A result of the Tor Uplift effort, this preference makes Firefox more resistant to browser fingerprinting.

Block outbound

browser.send_pings = false

The attribute would be useful for letting websites track visitors' clicks.

Disable Firefox prefetching pages it thinks you will visit next:

Prefetching causes cookies from the prefetched site to be loaded and other potentially unwanted behavior. Details here and here.

• network.dns.disablePrefetch = true
• network.dns.disablePrefetchFromHTTPS = true
• network.predictor.enabled = false
• network.predictor.enable-prefetch = false
• network.prefetch-next = false

Location bar

browser.urlbar.speculativeConnect.enabled = false

Disable preloading of autocomplete URLs. Firefox preloads URLs that autocomplete when a user types into the address bar, which is a concern if URLs are suggested that the user does not want to connect to. Source

Plugins

media.eme.enabled = false

Disables playback of DRM-controlled HTML5 content, which, if enabled, automatically downloads the Widevine Content Decryption Module provided by Google Inc. Details

DRM-controlled content that requires the Adobe Flash or Microsoft Silverlight NPAPI plugins will still play, if installed and enabled in Firefox.

media.gmp-widevinecdm.enabled = false

Disables the Widevine Content Decryption Module provided by Google Inc., used for the playback of DRM-controlled HTML5 content. Details

Hardware Fingerprinting

media.navigator.enabled = false

Websites can track the microphone and camera status of your device.

Persistent Storage

network.cookie.cookieBehavior = 1

Disable cookies. 2 is likely to break some sites. 4 is the default default. 1 is more strict than 4.

• 1 = Only accept from the originating site (block third-party cookies)
• 2 = Block all cookies by default
• 4 = Block Cross-site and social media trackers

Headers/Referers

network.http.referer.XOriginPolicy = 2

Only send Referer header when the full hostnames match. (Note: if you notice significant breakage, you might try 1 combined with an XOriginTrimmingPolicy tweak below.) Source

• 0 = Send Referer in all cases
• 1 = Send Referer to same eTLD sites
• 2 = Send Referer only when the full hostnames match

network.http.referer.XOriginTrimmingPolicy = 2

When sending Referer across origins, only send scheme, host, and port in the Referer header of cross-origin requests. Source

• 0 = Send full url in Referer
• 1 = Send url without query string in Referer
• 2 = Only send scheme, host, and port in Referer

Media

This may break some websites which use VOIP based features.

webgl.disabled = true

WebGL is a potential security risk. Source

Sessions and session restoration

browser.sessionstore.privacy_level = 2

This preference controls when to store extra information about a session: contents of forms, scrollbar positions, cookies, and POST data. Details

• 0 = Store extra session data for any site. (Default starting with Firefox 4.)
• 1 = Store extra session data for unencrypted (non-HTTPS) sites only. (Default before Firefox 4.)
• 2 = Never store extra session data.

Miscellaneous

beacon.enabled = false

Disables sending additional analytics to web servers. Details

network.IDN_show_punycode = true

Not rendering IDNs as their Punycode equivalent leaves you open to phishing attacks that can be very difficult to notice. Source

Safe Browsing

browser.safebrowsing.downloads.remote.enabled = false

Prevents Firefox from sending information about downloaded executable files to Google Safe Browsing to determine whether it should be blocked for safety reasons. Details

Firefox Android (Fenix):

First Party Isolation

These settings should be safe, however first party isolation may break some third party login systems.

privacy.firstparty.isolate = true

A result of the Tor Uplift effort, this preference isolates all browser identifier sources (e.g. cookies) to the first party domain, with the goal of preventing tracking across different domains. (Don't do this if you are using the Firefox Addon "Cookie AutoDelete" with Firefox v58 or below.)

Resist Fingerprinting

One of the features of resist fingerprinting is to set the reported browser timezone to UTC. If you depend on having your real time zone reported to the websites you visit, this setting may break that.

privacy.resistFingerprinting = true

A result of the Tor Uplift effort, this preference makes Firefox more resistant to browser fingerprinting.

privacy.resistFingerprinting.letterboxing = true

This sets the resolution of your Firefox window to a standard resolution. Only use this if you are using the above privacy.resistFingerprinting

Media

This may break some websites which use VOIP based features.

webgl.disabled = true

WebGL is a potential security risk. Source

Disable WebRTC

See WebRTC section

Firefox user.js Templates

• arkenfox user.js An ongoing comprehensive user.js template for configuring and hardening Firefox privacy, security and anti-fingerprinting. Desktop Firefox Only

Related Information

• Firefox Privacy: Tips and Tricks for Better Browsing - A good starting guide for users looking to keep their data private and secure.
• ffprofile.com - Helps you to create a Firefox profile with the defaults you like.
• Privacy Settings - A Firefox add-on to alter built-in privacy settings easily with a toolbar panel.
• Firefox Privacy Guide For Dummies - Guide on ways (already discussed and others) to improve your privacy and safety on Firefox.