Blocking Facebook in your Safari browser can prevent anyone from accessing the site through that browser. This can be a good way to keep kids from going on Facebook when they are not supposed to or to deter yourself from spending time on Facebook. You can disable Facebook in your Safari browser in the Mac's System Preferences. You will need to create a new account for the user; this new account will not be able to control which sites are blocked. After creating a new account, you can use the Mac's parental controls to block Facebook.