Enable Silent Printing

To enable silent printing:

Make sure the printer Firefox uses by default is the one you want to silently print to.

1. Type about:config in Firefox's location bar and hit Enter

2. Right click anywhere on the list that appears and select New > Boolean

3. Enter the name as print.always_print_silent, set the value to true and hit OK

4. Find print.show_print_progress, set the value to false and hit OK

From now on when something prints it will automatically be sent to the default printer.