Hacking Firefox: The secrets of about:config

By Serdar Yegulalp, Computerworld, 06/05/07

Ever since its debut, Firefox has garnered a reputation for being an enormously customizable program, both through its add-on architecture and its internal settings. In fact, many of Firefox's settings aren't exposed through the Tools > Options menu; the only way to change them is to edit them manually. In this article, we'll explore some of the most useful Firefox settings that you can change on your own, and that aren't normally available through the program's graphical interface.

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The closest analogy to how Firefox manages its internal settings is the Windows Registry. Each setting, or preference, is given a name and stored as a string (text), integer (number) or Boolean (true/false) value. However, Firefox doesn't keep its settings in the registry, but in a file called prefs.js. You can edit prefs.js directly, but it's often easier to change the settings through the browser window.

Type about:config in the address bar and press Enter, and you'll see all the settings currently enumerated in prefs.js, listed in alphabetical order. To narrow down the hundreds of configuration preferences to just the few you need, type a search term into the Filter: bar. (Click the Show All button or just clear the Filter: bar to get the full list back again.)

To edit a preference, double-click on the name and you'll be prompted for the new value. If you double-click on an entry that has a Boolean value, it'll just switch from true to false or vice versa; double-click again to revert to the original setting. Not all changes take effect immediately, so if you want to be absolutely certain a given change is in effect, be sure to close and reopen Firefox after making a change.

Note that not every setting in about:config exists by default. Some of them have to be created manually. If you want to add a new preference, right-click somewhere on the page and select New, then select the type of item to create (String, Integer or Boolean) and supply the name and value.

Before you begin

Here are a few caveats to keep in mind as you explore and tweak: