To uninstall the Inquisitor search (http://www.inquisitorx.com/safari/index_en.php) plugin from safari issue the following commands on the command line:

sudo rm -Rf /Library/InputManagers/Inquisitor/
sudo rm -rf /Library/Receipts/inquisitor*
rm -Rf ~/Library/Application\ Support/Inquisitor/

Quit and restart Safari