When you using e-kassa with Mozilla Firefox , you should disable the print headers and footers in browser settings. You also have to adjust the margins used by printing. This avoids unnecessarily printing the web address and other unnecessary text on the receipt.
Open the Menu on the right side of the Firefox -browser and select Print.
When the preview opens, click the Page Setup... -button on the left.
In the window that opens, select the Margins and Headers / Footers -tab. Then select blank in the Headers and Footers -section. In addition, change all margins to 0 (zero).
Then click OK and click Close to close the preview. After that, the receipt printing should working. Different receipt printers may require different values for margins. These values have been tested on the Citizen CT-S 310II receipt printer.