Mozilla Firefox About Config (about:config)

Mozilla Firefox provides the Configuration Editor via the about:config URL. The about:config is very popular in order to change configuration and preferences about the Mozilla firefox. The about:config data is stored inside the JavaScript files named prefs.js and user.js . The user configuration is stored in the user.js and the default configuration is stores in the pfres.js files. Even Mozilla Firefox GUI menus like Settings panel provides different preferences and configuration the about:config is the raw and fast way to change the configuration.

Open about:config

Opening the about config or Configuration Editor is very easy. Just type about:config to the address bar instead of the URL. The about is a special keyword which runs provided keywords as native Firefox keyword. And the config specify the configuration.


We see the following screen as we open the raw editing mode for Firefox and this is an advanced configuration mode that can impact Firefox performance and security. Just click to the Accept the Risk and Continue . Alternatively, uncheck the Warn me when I atempt to access these preferences checkbox to skip this warning in the next attempts.

Open Firefox about:config

Show All Preferences

After opening the about:config or Preferences screen we see just a search box and there is no preference or configuration is listed. We can click to the Show All button in order to list all Firefox preferences and configuration.

Show All Preferences

Search Preference

Mozilla Firefox provides a lot of configuration and preference options. It is not feasible to find a configuration by searching the eye. The best, fast and easy way is using the search box about the preferences and configuration. A configuration can be searched via this search box.

  • Preference names are case-sensitive which means uppercase and lowercase letters are different and do not matches.
  • Search term may match in different parth of the preference or configuration name. For example when we search for ftp it matches network.ftp.control.qos and network.proxy.ftp
Search Preference

Modify Preferences

The preferences or configuration values can be changed or modified easily by double-clicking the value part of the configuration like below. Set the value you want to set. Boolean, Number, and String values can be used according to the preference requirement.

Modify Preferences

Reset Preference Value

When the default value of the preference is changed an icon appears on the right side like below. This icon can be clicked to reset to the default value provided with the Mozilla firefox.

Reset Preference Value to Default

Add Preference

A new presence can be added by using the search box. Just type the preference name you want to add which is listed with the Boolean, Number, and String types. Select the type of preference which is String in this case. The last step is to click to the + plus sign to add it.

Add New Preference

After the preference is added it is displayed like below with its default value which is 0 for number. We can set the value whatever we want and click on the check sign on the right.

Set New Preference Value

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