I think I'm fighting a losing battle. Does anyone know if there's an about:config setting (or user_pref() from user.js) that I can set to allow certain domains to use user_pref() in JavaScript? Reason: I'm writing an AJAX app that needs to use 2 printers - one for labels, one for reports. I've disabled the print dialog using the about:config setting "print.always_print_silent" so that labels are printed immediately. I need to be able to select the report printer automatically as the print dialog is no longer displayed - this can be done by setting the about:config setting "print.print_printer", but as I need it to be done on the fly, I'll need to call user_pref() which isn't allowed outside of XUL. If no one can think of a solution I'll have to use XUL to do it