Enterprise Software

SolutionBase: Customize Firefox using about:config

One of the best things about Firefox is its flexibility and extensibility. Here's how you can tweak settings inside of Firefox using <i>about:config</i>.

This article is also available as a TechRepublic download.

Internet surfers everywhere seem to be taken with Mozilla's browser offering, Firefox (now in release 2.0.x). This is partly due to the browser's speed and extensibility; but Firefox also has the ability to completely customize its configuration. This article will cover the last of Firefox's hidden pages, about:config and some of the tweaks it allows the user to make.

Accessing the configuration

To access the guts of the Firefox browser, enter about:config into the Address bar and press [Enter]. This will bring up a long list of customizable preferences for the current installation of the browser. The default configuration is similar the one shown in Figure A.

Figure A

Some options available in the default configuration of Firefox.

The items within the configuration file that have been user modified are shown in bold type with a status of User Set. Many of the options shown above are configured by the installation process, but can be modified to your liking.

When you open the configuration page you will find a filter box which allows you to find only certain parameters within the configuration. This makes the task of finding the items you want to change a little easier than sifting through the enormous list of preferences. To use the filter bar (shown in Figure B), type a portion of the preference name in the box and press [Enter]. Figure B also shows the filtered results for Google that are present in the configuration file.

Figure B

Filtered preference list.

Now that we have looked at the available tools for editing the configuration, we can get into the actual capabilities available to the user for customizing the Firefox experience.

As an example for this article, I will change a few settings within about:config; keep in mind that there are many customizable settings. You should also be aware that some settings may cause the browser to perform unexpectedly.

What items will the about:config page display?

When you visit the list of preferences kept in about:config, you will see the following columns for each item listed:

  • Preference Name: Lists the name of the configuration item.
  • Status: The current status of a preference will be set to user set by Firefox when the value is changed by the user.
  • Type: Shows the type of data this preference expects.
  • Value: Displays the current value of the preference; when customizing preferences, you will only edit the value portion of each option.

There are preferences for almost everything Firefox does that can be modified. You can also add your own preferences to the about:config file. Remember, this browser is all about the user and the user experience, from performance to appearance.

Modifying existing preferences is the easiest way to familiarize with the configuration system used by the browser. The settings available from the Tools | Options menu are also configurable from the configuration screen. Let's change the Start page using about:config to point to http://www.techrepublic.com.

First, open about:config by typing the address in the Address bar and pressing [Enter]. After the page opens, enter the word startup in the filter box and press [Enter]. This will return all of the preferences where the name contains startup.

The preference for the homepage is browser.startup.homepage; the default Google.com-powered start page is displayed as resource:/browserconfig.properties. To modify this item to point to TechRepublic.com, double-click the preference and in the dialog box that pops up, enter http://www.techrepublic.com and press OK, as shown in Figure C.

Figure C

Changing the start page within Firefox from about:config.

Once you press OK and save the new value, the configuration file will change the status to user set. If you open a new tab in the browser window and then press the Home button, you should be immediately whisked away to TechRepublic's home page.

While some changes like the homepage take effect immediately, other changes may require a restart of the browser application. Firefox does not tell you if a restart will be required for preference changes.

Tabbed startup pages

We could also take advantage of Firefox's tabbed browsing capabilities and open multiple tabs as a homepage when the browser opens or the home button is clicked. To use a tabbed start page, you can enter the URL's of the pages you wish to open, separated by a pipe symbol. After pressing OK, all of the pages you entered should open in tabs when you open a new Firefox window.

I will use http://www.techrepublic.com | http://www.google.com | http://www.microsoft.com as my value for browser.startup.homepage; this is shown in Figure D.

Figure D

A tabbed start page.

These settings produce a three-tab window when a new window is opened, as shown in Figure E.

Figure E

The home page tabs opened within a new window.


Modifying the start page is a rather easy example; you have much more power available when modifying Firefox settings. With this browser, if there is a setting for something, you can probably configure it within about:config without too much trouble.

Usually, when looking through the list of preferences, the name of the item will give you an idea of what it will affect. As with browser.startup.homepage, the browser object has a startup property which has preferences — homepage being one of them — that can be changed here.

Another example of a preference that you can modify is browser.tabs.warnOnClose. This preference will turn the dialog box shown in Figure F on or off; the box appears when closing a window containing multiple tabs. By default, Firefox will warn you when you close a window that contains multiple tabs; about:config allows this setting to be disabled.

Figure F

Warning: you are closing multiple tabs.

Notice that the dialog box above has a check box that can be set to warn you when you close multiple tabs, when you change the value on the dialog box to unchecked, or when the status of the browser.tabs.warnOnClose preference in about:config is set from true to false. You could also make that change directly from about:config.

Lots of settings

About:config can also control settings which are not always immediately visible to the user. You can set scrolling options for a wheel mouse, the path of an external editor for use with Firefox, or even set the expiration time of the master password; all of these settings — and many more — are user-editable.

Many third-party extensions to Firefox will also make new entries into about:config as they are installed. These preferences can also be customized. You can experiment if you want; but, for third-party extensions, it is a good idea to test and reset the preferences that change to the default, just to make sure they continue to work.

The best recommendation I can make — without giving examples for each of the many preferences available in about:config — is to look through the file and see which settings might make your experience better. The best thing to do is get in there and get your hands dirty. Experiment with your browser and see what type of user experience you can create.


Derek Schauland has been tinkering with Windows systems since 1997. He has supported Windows NT 4, worked phone support for an ISP, and is currently the IT Manager for a manufacturing company in Wisconsin.

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