How to use the About:Config feature.

1. Start Firefox.
2. Type about:config into the address bar and press Enter. When you’re presented with the warning screen click the I’ll be careful, I promise button
3. You should see a long list of hidden settings that look meaningless and confusingly complicated
4. Now comes the fun part of actually modifying and/or creating new values:
   • If I tell you that the key already exists then you can type the name of the preference in the Filter box, and it will instantly show only the matching results. Once you find the preference you’re looking for just double-click on it to change the value.
   • If I tell you that the key does not exist you will need to create a new value manually. Don’t be intimidated… it’s not as difficult as it sounds. Just right-click on any entry on the about:config screen, go to the New menu, and choose either string, integer, or boolean depending on what I tell you.
     
     
5. You may need to restart your browser for some of the options to take effect.
6. Wanna go back to the way something was before you tweaked it? Any of the preferences can be reset to their default values in the event that something doesn’t work the way you expected it to. This can be done by right-clicking on the particular option in about:config, and selecting Reset. Values that have been changed at one point or another will appear in bold text, and once they have been reset they should no longer be bold.