set print settings in user.js

[murray bryant]

I am tring to set global print settings in the user.js file, so that 
when a user uses another printer all of the settings remain the same.

I have tried this

user_pref("print.print_margin_bottom", "0");
user_pref("print.print_margin_left", "0");
user_pref("print.print_margin_right", "0");
user_pref("print.print_margin_top", "0");
which does not work. Does anyone know of the correct synax to force 
mozilla to set the settings?

Thankyou

Murray