Moth balls are made up of either napthalene or paradichlorobenzene. Both of these are hydrocarbons, which is what most of the molecules in gasoline are. I'm not familiar with anyone ever running an octane number on either of these. Neither of these appear, chemically, to have much octane boost potential. Their use (mothballs) seems to stem from the '20's or '30's. If in fact they did have some benefit it would probably take a lot of them to show any improvement. Plus, since they are a solid at room temp you would probably need to be concerned about preciptation in the carb or injection system during storage.
Here are a couple of links describing each chemical. Not nice stuff!

http://home.howstuffworks.com/framed...l/Naphthal.htm

http://home.howstuffworks.com/framed...l/14-dichl.htm