You can now edit your friends list. This will shortly also be available via a button in users.js.
From that page you can add other users as friends by entering their High Fidelity username. You can remove anybody you have previously made your friend by clicking on their name in the list.
Via users.js and using the latest Interface client - if you switch to ‘friends only’ mode, only the people shown in this list will be able to see that you are online and jump to you.