If you like the idea of printing receipts automatically, but don't love Firefox print dialog box that pops up after a transaction, good news! There is a way to bypass this setting, but it will take a little bit of configuration.
IMPORTANT: This option is best if you only have a single printer connected to the computer you are working on. If you are regularly switching between printers at a station, having that dialog box pop up every time is likely a better option, so we would highly recommend NOT doing this with multiple printers connected.
* To switch between printers, you will need to change your default printer. This is a system setting and can be changed under your printer settings.
NOTE: If you need to change it back so that the print dialog box does come up, repeat the first step below, find 'print.always_print_silent' in the list, right-click on it and click Toggle to change it to False (off).
Open Firefox and type 'about:config' in the address bar and press enter. Click to confirm that you will be careful.
Right click on the page, hover over 'New' and click on 'Boolean'.
Type 'print.always_print_silent' as the preference name and click 'OK'.
Click on 'true' and click 'OK'.
That's it, the print dialog boxes will no longer pop up for you!