Are you using Health Check or Custom Clean? Health Check uses its own settings and will always clear Firefox history. If you don't want to do that then you have to use Custom Clean and untick Firefox history. Those tick/untick settings apply only to Custom Clean. (They will not be respected by Health Check which always uses it's own settings). If you want to set Custom Clean as the default mode for CCleaner then go to Options>Settings and change the CCleaner Home Screen.