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.
If you’ve never edited your Firefox via about:config, then you have no idea what you are missing out on. Not that there is anything life-changing in there, but some of the most simple option changes can make a big difference in your surfing experience.
Source: Computer World