The user preferences are stored as JSON, which is not very accessible. We should add a UI for setting them to the player. Changes can then be written to the preferences page without the user even having to see it. How nice we make it is a matter of how much time we want to invest. A simple popup dialog using OOUI should not take too long.
The popup dialog should include a note that the page needs to be reloaded for the preferences to take effect.