how can i get out private browsing for ever,so nobody can use it from my pc

Mozilla have not provided an option to turn off private browsing. You can hide the menu items but that will not stop somebody from accessing it by using the keyboard shortcut. For details on how to hide the menu items see this thread - [https://support.mozilla.com/tiki-view_forum_thread.php?comments_offset=0&comments_threadId=0&comments_parentId=576657&comments_threshold=0&thread_sort_mode=commentDate_asc&forumId=1&time_control=3600#threadId576657 How do i block the private browsing option from my children?] Even with the menu items removed, it does not stop anybody from using the clear recent history option to remove traces of sites that they have visited.