Schiwi , currently your player is working, so i wouldn't encourage you to try any firmware updates. Likely chance of killing your player while doing so.
However, if you are adventurous and want to try to enable the file-browsing. Extract your firmware and keep it safely for backup first. Next, read up on Rolleyflex's thread on merging firmware
Here.
But bear in mind that if you accidentally kill your player, there is still a slight chance that you might not find the right Full firmware to bring your player to ADFU state.
Good Luck.