please somebody tell me
That doesn't delete it completely, when you search, there are hidden files saved to your computer - index.that files, which you cannot delete. And are easily accessible if you know what you are doing.
Sorry... but you can't completely get rid of them.
Nothing is ever a sure fix, there is almost always a trace and a good forensic tech can find those traces and even recover deleted information sometimes, but if your just trying to shield the common user from seeing you tracks ccleaner works well.
Take a read through the answers there...in firefox, it's view - history - then select clear / delete all.