Laito , currently these nano-clones do not support file-browsing, only supports folder browsing. However, there is a thread by ROLLEYFLEX
Here that explains merging of firmwares to enable the file browsing feature sometime back.
But be warned that incorrectly merged firmwares would definitely kill your player! If you should decide to go ahead with the firmware merging, always make a backup of your existing firmware.
Besides that, there is nothing much really you could do to enable it. Never ever update with someone elses firmware, you have a high chance of killing your player.