Open about:config again and in the filter at the top, type: babylon
For every setting you find with that name in it, right click it and choose Reset.
For the following settings which might also have the word "babylon" in them, right click and choose "Modify". Then delete "babylon" and replace it with the word Google if a reset doesn't do that automatically.
Then close Firefox via File | Exit and restart it again.
Check the keyword.URL though to add the link to Google again if necessary.