I know what you are thinking… why would you possibly want it back?
If you are customizing Firefox for somebody else and you turned the warning off… you might want to re-enable it after you are done to help prevent them from making changes.
Re-Enable about:config Warning
Type in about:config into the address bar, and then filter by the following:
Just double-click on the item to change the value back to true, and the warning message will show up again.
