The about:config menu is a powerful tool for tweaking the Firefox browser. Entering about:config into the Firefox address bar opens up a bevy of application settings for everything from removing the "close tab" button (browser.tabs.closeButtons) to including the punctuation when you double-click on a word (layout.word_select.stop_at_punctuation).
However, installing and uninstalling extensions can create a number of about:config entries that no longer apply to your Firefox setup. You can create your own application-setting entries easily in about:config, but how do you remove the entries you no longer want or need?
Well, it's not easy, but it's certainly doable. Unfortunately, you'll have to delve into the "Application Data" directory of Windows. Open Windows Explorer and navigate to Documents and Settings -> [your username] -> Application Data -> Mozilla -> Firefox -> Profiles -> [your profile].
On Mac OS X, you'll need to get into your profile setting via: [your username -> libraries -> Firefox -> profiles ->[your profile]. For both Windows and Mac, if you only have one profile, it might be named something odd, like "32kjfs0c.default."
In your profile directory, you should see a file named "prefs.js" which stores most of your preferences. Open this file with your favorite text editor. Do you see long URL strings? That's your session saver at work!
Each about:config setting corresponds to a line of the prefs.js file and that file will update accordingly based on your Firefox behavior. That's why you'll need to close Firefox first before making any changes. If you make changes with Firefox open, the browser will overwrite your changes when it quits. (It even says that in the prefs.js file in case you forget.)
Find the entries in prefs.js that you want to remove from Firefox, delete each entire line, and then restart your browser. Voila. The deleted entries should now be gone from your about:config screen.
For example, I've tested out the Pong Multiplayer extension in the past, because it was just too darn cool to play Pong in the Firefox browser. However, I no longer use it, so the 55-odd application settings for it are just cluttering about my about:config screen. When I go into my prefs.js file, I can see:
user_pref("extensions.pong.chattemplate5", "Game on!");
etc. etc. x50
Just deleting those 50-plus lines from the prefs.js file gives me a slightly cleaner about:config screen the next time I fire up Firefox.
Is it essential to clean out these unused application settings? No. They won't likely slow down your browser at all, but they definitely make it more difficult for me to navigate through my Firefox settings. For the slightly obsessive-compulsive Firefox user, it's a necessary tweak. No clutter!