How to configure Firefox programmatically

I reinstalled Ubuntu on my personal computer recently and I noticed that there are some things I don’t like about the default distribution. One of the things I noticed is that Firefox keeps asking me if I want it to remember my passwords, which I don’t.

I know that I can go to settings and disable this feature, but I wanted to learn how to do it programmatically, so in the future I can just run a script and have Firefox work the way I want.

Preferences

There is documentation explaining how preferences work for mozilla projects, but it’s a little hard to understand how to exactly do what I wanted to do.

When Firefox is loaded, there are a few preferences files that are loaded. The combination of these files determine the configuration that Firefox will use for that run.

When a user makes a change to a Firefox preference via the UI, the change is written to prefs.js. This file should never be edited manually because changes might get overwritten. To get a UI where you can modify any preference you can enter about:config in Firefox URL bar.

For custom configurations we can write our desired changes to one of two files:

• all-<something>.js - Sets configurations for all users in that host
• user.js - Sets configurations for a specific user

The all-<something>.js method is usually preferred because a user might want to set their own preferences. If user.js method is used, anything they set will be overwritten by the values set by the administrator on every Firefox run.

Setting preferences

The tricky thing for me was finding where the all-<something>.js file should live. The documentation says install_directory, but it wasn’t clear to me where this was for Ubuntu. It turns out, the install directory is: /usr/lib/firefox/.

To set a preference we can use the pref() method. I created a bash script to do this for me:

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# Configure firefox
ff_preferences="/usr/lib/firefox/browser/defaults/preferences/all-company.js"
touch $ff_preferences
echo "pref('signon.rememberSignons', false);" >> $ff_preferences

Finding preferences

Finding which preference to change can also be tricky. The best I could find is a list of preferences with short descriptions, but it can be hard to find what you are looking for.