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Hacking Firefox: The secrets of about:config

Discover more than 20 behind-the-scenes tweaks for speeding up page loads, reducing memory drain and making the interface behave the way you want it to

By Serdar Yegulalp
May 29, 2007 12:00 PM ET

Computerworld - 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.

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.)

The about:config page.

The about:config page. (Click for larger view.)

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.

Editing a preference.

Editing a preference. (Click for larger view.)

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:

Not everyone will get the same benefits by enabling these tweaks. This is especially true for changing the network settings. If you habitually visit sites that don't allow a large number of connections per client, for instance, you won't see much benefit from raising the number of connections per server.

Some hacks may have a limited shelf life. With each successive release of Firefox, the need for tweaking any of the performance-related config settings (like the network settings) may dwindle as Firefox becomes more self-tuning based on feedback from real-world usage scenarios. In short, what works now may not always work in the future -- and that might not be a bad thing.



 
Keep a log of everything you change, or make backups. If you tweak something now and notice bizarre activity in a week, you'll want to be able to track back to what was altered and undo it. Firefox does show which about:config changes have been set manually, but this isn't always the most accurate way to find out what you changed.

To make a backup of your preferences in Firefox, just make a copy of the file prefs.js, which is kept in your Firefox profile folder. If you mess something up, you can always copy this file back in. (Be sure to shut down Firefox before making a copy of prefs.js or moving a copy back into the profile folder!)

In Windows XP, the profile folder is
\Documents and Settings\<username>\Application Data\Mozilla\Firefox\Profiles\<profile ID>.default\

In Windows Vista, this folder is
\Users\<username>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile ID>.default\

Note that Application Data and AppData are hidden folders by default, so they may not show up unless you force Explorer to show hidden objects. (Open the Control Panel, double-click Folder Options, select the View tab, select "Show hidden files and folders" and click OK.)

In Mac OS X, the profile folder is
<username>/Library/Application Support/Firefox/Profiles/<profile ID>.default/

and in Linux it's
~/.mozilla/firefox/<profile ID>.default/

but on those platforms it's usually quicker simply to search for prefs.js.

Alternatively, you can use the handy Firefox Extension Backup Extension (FEBE). It backs up not only the prefs.js file but just about every other thing in Firefox -- extensions, themes, cookies, form history and so on.



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