Register at the EpsonExpert Technical Resource Center website to gain access to the drivers; go to Technical Resources, then choose the printer model from the Printers drop-down list.
Under File » Page Setup:
Shrink to fit page on Format & Options tab
0,0,0,0 for Margins on Margins & Header/Footer Tab. This makes the receipts use all available space on the paper roll.
Set all Headers/Footers to -blank-. This removes all of the gunk you might normally find on a print from firefox, such as the URL, number of pages, etc.
Set the default printer settings in Firefox so you don't see a "Print" dialog:
Go to File -> Print
Set the Printer to the receipt printer.
Print whatever page you are on.
Type about:config, in the address bar. Click "I'll be careful, I promise!" on the warning message.
Type, print.always in Filter.
Look for, print.always_print_silent.
If the preference is there then set the value to true.
If the preference is not there (and it shouldn't be in most browsers) you have to add the preference.
Right click the preference area and select New -> Boolean
Type, print.always_print_silent in the dialog box and set the value to True. This sets the print settings in Firefox to always use the same settings and print without showing a dialog box.
Setting the print.always_print_silent setting in about:config DISABLES the ability to choose a printer in Firefox.