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Firefox hardening with Arkenfox

Written by Solène, on 24 September 2023.
Tags: #firefox #security #privacy

Comments on Fediverse/Mastodon

1. Introduction §

Dear Firefox users, what if I told you it's possible to harden Firefox by changing a lot of settings? Something really boring to explain and hard to reproduce on every computer. Fortunately, someone did the job of automating all of that under the name Arkenfox.

Arkenfox design is simple, it's a Firefox configuration file (more precisely a user.js file), that you have to drop in your profile directory to override many Firefox defaults with a lot of curated settings to harden privacy and security. Cherry on cake, it features an updater and a way to override some of its values with a user defined file.

This makes Arkenfox easy to use on any system (including Windows), but also easy to tweak or distribute across multiple computers.

Arkenfox user.js GitHub project page

Arkenfox user.js Documentation

2. Setup §

The official documentation contains more information, but basically the steps are the following:

  1. find your Firefox profile directory: open about:support and search for an entry name profile directory
  2. download latest Arkenfox user.js release archive
  3. if the profile is not new, there is an extra step to clean it using scratchpad-scripts/arkenfox-cleanup.js which contains instructions at the top of the file
  4. save the file user.js in the profile directory
  5. add update.sh to the profile directory, so you can update user.js easily later
  6. create user-overrides.js in the profile directory if you want to override some settings and keep them, the updater is required for the override

3. Configuration §

Basically, Arkenfox disables a lot of persistency such as cache storage, cookies, history. But it also enforces a canvas of fixed size to render the content, reset the preferred languages to English only (that defines which language is used to display a multilingual website) and many more changes.

You may want to override some settings because you don't like them. In the project's Wiki, you can find all Arkenfox overrides, with the explanation of its new value, and which value you may want to use in your own override.

Arkenfox user.js Wiki about common overrides

For instance, if you want to re-enable the cache storage, add the following code to the file user-overrides.js.

user_pref("browser.cache.disk.enable", true);
user_pref("privacy.clearOnShutdown.cache", false);

Now, run the updater script, that will verify that Arkenfox user.js file is the latest version, and will append your override to it.

4. Tips §

By default, cookies aren't saved, so if you don't want to log in every time you restart Firefox, you have to specifically allow cookies for each website.

The easiest method I found is to press Ctrl+I, visit the Permissions tab, and uncheck the "Default permissions" relative to cookies. You could also do it by visiting Firefox settings, and search for an exception button in which you can enter a list of domains where cookies shouldn't be cleared on shutdown.

By default, entering text in the address bar won't trigger a search anymore, so instead of using Ctrl+L to type in the bar, you can use Ctrl+K to type for a search.

5. Extensions §

Arkenfox wiki recommends to use uBlock Origin and Skip redirect extensions only, with some details. I agree they both work well and do the job.

It's possible to harden uBlock Origin by disabling 3rd party scripts / frames by default, and giving you the opportunity to allow per domain / globally some sources, this is called the blocking mode. I found it to be way more usable than NoScript.js.

uBlock Origin blocking mode documentation

6. Conclusion §

I found that Arkenfox was a bit hard to use at first because I didn't fully understand the scope of its changes, but it didn't break any website even if it disables a lot of Firefox features that aren't really needed.

This reduces Firefox attack surface, and it's always a welcome improvement.

7. Going further §

Arkenfox user.js isn't the only set of Firefox settings around, there is also Betterfox (thanks prx!) which provides different profiles, even one for performance. I didn't try any of these profiles yet, Arkenfox and Betterfox are parallel projects and not forks, it's actually complicated to compare which one would be better.

Betterfox Github project page