You can confirm the firmware version by printing the printer settings report.
To print the printer settings report:

1. Turn the printer on and make sure no paper is loaded.
2. Press and hold the  (Feed) button until the DATA indicator lights in red.
3. Insert a piece of genuine Brother thermal paper into the printer’s paper input slot.  The report will print automatically, and then the printer will return to the idle mode.
4. Check the "PROGRAM VERSION" for the printer's firmware version.