Firefox 3.0.2 stores 'some' data on web sites visited in C:\Documents and Settings\............\Application Data\Mozilla\Firefox\Profiles\...........default\places.sqlite. CCleaner 2.12.651 ignores this location when cleaning Firefox.
places.sqlite stores both history and bookmarks, so just deleting the entire file would be a bad idea.
CCleaner would need a way to selectively delete the history.