If you have ever used the ‘about:config‘ screen in Firefox, then you would know that it is quite similar to the Windows’ Registry, for, it contains important information and settings. Fiddling with about:config, without knowing what you are doing could adversely affect Firefox. Of course, it may not be as catastrophic as when you mess up with your Windows’ Registry.

• First close down Firefox if it is running.
• Go to Start>Run and type %appdata%\mozilla\firefox\profiles and hit <Enter>.
• The resulting explorer window that opens will contain a folder with a peculiar name like ud732v0a.default. The actual folder name that you see will most probably be different, but the name will resemble something like this.

• Open the above folder and among other files you will find a file called prefs.js. This is the file we are looking for. Just copy it to a safe location. Should you mess up something in ‘about:config’, simply close Firefox and copy the backup of prefs.js back to its original location.