Firefox Config File

Firefox preferences (e.g. toolbar layout) can be saved within a config file.

Locate Your Profile Folder

Config files are stored within a profile folder. Locate your profile folder by entering about:profiles. Here you may see a few profiles. The one you want is the one with Default Profile set to Yes. The Root Directory shows you the location of you profile folder.

On a Linux system, the location of a profile folder looks like:

/home/<user>/.mozilla/firefox/<random-char>.default-release

Set Preferences with a Config File

Firefox preferences set within the UI are saved in prefs.js in your profile folder. This file must not be edited by hand. In the file, each line with user_pref(...) is a preference setting.

If you wish to set preferences with a file:

• Create a file user.js in your profile folder
• Add the preferences you wish to set in user.js. You may refer to preference settings from prefs.js

The preference settings in user.js takes precedence over prefs.js.

This could be a good way to transfer Firefox preferences from one device to another.

Related links:

• https://kb.mozillazine.org/User.js_file
• https://unix.stackexchange.com/questions/727999/which-files-can-be-used-to-configure-firefox-on-linux-mint-21-where-are-they-st