I contacted Panasonic by email and this is the reply they sent me:
The firmware download simply improves the overall performance of the unit.
If we can further assist you, please call the Panasonic Customer Call
Center 1-800-211-PANA. For your convenience, the call center is open from
9:00 am to 9:00 p.m. (est.; Mon-Fri) and from 10:00 am to 7:00 p.m. (est.;
Panasonic Consumer Support
Panasonic did not not provide any real information about what the firmware upgrade does.