how do I get rid of play sushi; I unistalled firefox but it still exist

I don't know how fire fox got on our computer (we are not computer literate). We use adware also that a computer friend told us about to help keep from getting viruses. it keeps showing play sushi as a problem. it says to go to firefox tools addon play sushi to unintall. I can't find tools. We uninstalled firefox awhile back. How do I get this off.