To enable silent printing in Firefox so no print dialog will appear, you have to change Firefox's config settings. You have to promise to be careful! Cutting Edge staff can't assist you if Firefox breaks.
- Type about:config at Firefox's location bar and hit Enter.
- Right click (or control-click) anywhere on the page and select New > Boolean
- Enter the preference name as print.always_print_silent and click OK. (You must be careful to spell it correctly, so copy and paste)
- In the next box set it to true
Note: The default printer will be used when printing via this method. You won't get a chance to change it. If this causes problems you can toggle it off by setting it to false - just right- or control-clicking on the line.