I believe you have an incorrect impression about what Private Browsing does. https://support.mozilla.org/en-US/kb/private-browsing-browse-web-without-saving-info

You may also wish to consider setting up a separate Operating System account for each user. One effect of that is that each user will then have a separate Firefox profile. *[[Profiles - Where Firefox stores your bookmarks, passwords and other user data]] * http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/ua_user_add.mspx * http://windows.microsoft.com/en-gb/windows/create-user-account#create-user-account=windows-8 * http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/windows_security_whynot_admin.mspx If you wish to use software that you hope will make browsing safer it is quite possible to do that only on your son's account but not your husbands. I think this addon should be capable of locking private browsing off * https://addons.mozilla.org/en-US/firefox/addon/cck/