[Tip] Reset or Restore About:Config Settings to Default in Mozilla Firefox

Recently an AskVG reader contacted me and asked how to reset all default settings in about:config page of Firefox? Actually he installed some 3rd party extensions in Firefox which started causing issues. He also modified many preferences in about:config page as mentioned on various websites claiming to speed up Firefox which were also causing weird issues while browsing websites. The reader uninstalled the extension but it didn’t fix the issue. Since he modified several preferences/flags in about:config page, he didn’t want to reset them one by one manually. He wanted a quick and easy way to restore all default preferences/settings in about:config page at once.

Actually it’s quite easy to reset all modified preferences/flags in about:config page to factory default without any need to restore them one by one manually. Today in this article, I’m going to share this trick.

If you are also facing issues after modifying preferences in about:config page (such as Firefox is no longer starting or crashing at startup) and you also want to reset about:config page in Firefox and want to restore all modified preferences to default, following steps will help you:

First of all, if you don’t know let me tell you. About:Config is an advanced configuration page present in Mozilla Firefox web browser which allows users to modify hidden secret preferences/flags which are generally not available in Firefox Options (about:preferences) page. About:Config page is an advanced tool developed for experts so that they can customize Firefox according to their requirements. Most of the times, About:Config page is used to enable or disable features in Firefox. We have shared lots of tutorials in past which utilize About:Config page in Firefox.

More Info: [Tip] Access Hidden Secret Advanced Configuration Page in Your Web Browser

Whenever you modify any preference/flag using about:config page in Firefox, it actually stores the preference along with its value in Prefs.js file present in the user profile folder. When you install Firefox, it automatically creates a user profile folder for you to store your preferences, browsing history, bookmarks, passwords, etc.

More Info: All About Mozilla Firefox Profile Folder and Configuration Files

Prefs.js file stores all default and user modified preferences of About:Config page and whenever Firefox launches, it reads this file to load features according to the preferences mentioned in the file.

Similar to Prefs.js, there is another file in Firefox called User.js. This file is not present by default but users can create this file to store their modified preferences. User.js file is used to override preferences mentioned in Prefs.js file.

To reset all modified preferences/flags in About:Config page, you just need to delete both files Prefs.js and User.js (if present). Once you delete these files, Firefox will restore all preferences/flags in about:config page to default.

Now the question comes, how to delete these files? Here are the steps:

1. Open Firefox and click on Firefox Menu (hamburger menu) button and select Help -> Troubleshooting Information option. You can also directly open it by typing about:support in addressbar as mentioned here.

2. It’ll open Troubleshooting Information page. Now click on “Open Folder” button given next to “Profile Folder” label.

It’ll open your Firefox profile folder directly which is usually present in “%appdata%\Mozilla\Firefox\Profiles\” folder.

3. This step is important! Close Firefox. If you don’t close Firefox and delete Prefs.js file, Firefox will restore the file with same values. So close Firefox.

4. Now look for Prefs.js and User.js files in profile folder. By default, you’ll only see Prefs.js file as it’s created by Firefox in all computers. User.js file needs to be created manually by the user, so if you didn’t create it manually, you’ll not see it in your Firefox profile folder.

PS: Before deleting Prefs.js and User.js files, make sure to take a backup of these files so that you can restore them in future if required or if you are not satisfied with the result. To take a backup, copy the files to some secure location such as Desktop or a different drive where you can easily access them.

5. Now select Prefs.js and User.js (if present) files and delete them.

PS: Firefox will automatically create a new Prefs.js file in profile folder for you as soon as you launch it.

That’s it. Now launch Firefox and open about:config page and all preferences/flags will reset to default. You’ll not see any modified setting.

In future, if you want to restore your previous customized settings in about:config page, replace new Prefs.js file with your old Prefs.js file (backup) in profile folder.

BONUS TIP:

If you want to full reset Firefox browser to default settings i.e. remove all extensions, restore factory settings, clear history/cookies/etc, you just want to fresh start Firefox, following tutorial will help you in resetting Firefox as well as other popular browsers to default:

[Tip] How to Reset / Restore Your Web Browser Settings to Default Factory State

TIP for Google Chrome Users:

Similar to Firefox, if you want to reset or restore all modified preferences/flags in Chrome://flags page in Google Chrome web browser, following tutorial will help you:

[Fix] You Enabled Some Flags on Chrome://Flags Page and Google Chrome No Longer Opens

Also Check:

[Tip] How to Restore Old About:Config Page in Mozilla Firefox