Here’s what you need to do to enable Firefox to immediately print without showing the print preferences dialog box.

  1. Type about:config at Firefox’s location bar and hit Enter.

  2. Right click at anywhere on the page and select New > Boolean

  3. Enter the preference name as print.always_print_silent and click OK.

    That's it! From now on when you hit the print icon, there will be no need to go through the additional print dialog box. Save time!