Lock changes to preferences
Is there a way to lock "Preferences" in Safari so that no changes can be made by another user?
MacBook Air (13-inch, Early 2014), iOS 8.3
I'm not sure how you set up other users on your computer, but...
Each user should have his/her own account in System Preferences > Accounts.
This way, each user can set their own preference, if you, as the Administrator of the computer, allow them to do this.