I'm not really answering a reader's question today. But the trick I'm about to reveal is important to all Firefox users who like to get their hands dirty fiddling with settings. In fact, it's important to the tip I'm posting on Wednesday (which is why I decided to post it first).
Firefox saves your preferences and settings in a single place. Some of those settings you can alter in the Options dialog box, but not all of them. The others require going into an obtuse, difficult-to-understand work environment called about:config.
And if you play around in about:config, changing settings that you think you understand, you canreally mess things up. That's why, when you enter this environment--which you do byclicking the address bar (pressing CTRL-L will not work in this situation), typing about:config, and pressing ENTER--you have to click a button that reads "I'll be careful, I promise!"
In other words, this is Firefox's version of Windows' Registry--a powerful, yet difficult and dangerous place to play. And like the Registry, it should be backed up before you fiddle with it.
First, close Firefox. Then click Start (Start, then Run if you're using XP). Type %appdata%\Mozilla\Firefox\Profiles, then press ENTER. You'll probably find only one object in the resulting Windows Explorer window--a folder with a very weird name. Open that folder, and find a file inside called prefs.js. Copy that file to another location.
I repeat, copy that file. Do not move it.
You've backed up your Firefox settings. Now you can safely change them.
Should you ever botch something up in about:config and need to restore Firefox, close the browser, and copy that backup of prefs.js to its original location, overwriting the file that's there.