In Mozilla Firefox, you use the ‘about:config’ command to customize its configuration. if you misspell an entry when you are typing it in or you don't want the configuration you just added, you can use the following way to delete those entries:
To delete an entry, just right-click it and select Reset. Then, restart Firefox. If the value you chose was originally part of the browser, it will go back to its default value. If the value was added by you, it will be deleted.
