Yes Mothballs do keep squirrels away since the Mothballs put out a scent that squirrels hate and will keep the squirrels away.
You can place the mothballs in places that squirrels are being a problem such as the attic or anywhere else and the squirrels will stay away from those areas.
You'll need to replace the mothballs every few weeks though because they eventually become ineffective and lose their scent but if you keep replacing the mothballs with new ones every few weeks then the squirrels will stay away.
Coffee Grounds are also another good natural deterrent to repel squirrels since the used coffee grounds put out a scent that we love but the squirrels hate the smell of used coffee grounds and will leave the area when they come to areas that the coffee grounds are placed.