Thanks. Yes, Upgrading to 5.4 replaced both Firmware 1 and Firmware 2 at the same time.
This means that now I have only 5.4 installed and it is not dual-boot with 5.3 (I expected it to be this manner again)
On the other side, having the ability to boot from both firmwares was a good idea. It is useful for a limited time that someone may decide whether the change is suitable or not. Afterwards, lets say after a month or two could delete the unnecessary one (either newer / older) to reduce maintenance confusions.