A useful feature when using ShopTill-e ePOS in full screen mode, is to use Silent or Background Printing...
To enable Silent /Background Printing in Firefox to print without showing the print preferences dialogue box.
1. Type about:config in Firefox’s address bar and hit Enter.
2. Right click anywhere on the page and select New > Boolean
3. Enter the preference name as print.always_print_silent and click OK. Set to true (using the 'toggle option = right click and select toggle from the menu or simply double click on the rule) see:
Alternatively, you can consider using and add-on / extension such as 'Silent Print '
Also please see - Google Chrome Kiosk Mode with Background / Silent printing