Hey, Each Firefox user has to have read/write access to the [[profiles|profile]] directory to be able to perform basic browsing functions including Firefox saving the history itself. Unfortunately even if you remove any graphical ways to enter private session or clear history, the profile data are easy to delete manually. This is why your request is not as easy as it can seem. A possible solution would be to set the modem/router to log every website accessed and password-protect its administration page. Some routers do have this functionality, and you also can use them to block specific websites.