This is almost certainly not a firefly thing — it only ever opens music files as read-only, so even if it hangs or something, it shouldn’t corrupt the file system.
The hang may well have been the usb stick. Did you set up the usb to minimize writes to flash, and move the firefly db off the flash and onto the usb? That will probably help flash longevity.
No, you are right… will try this night..
btw (I know this is a slug thing, not firefly) when the flash get corrupted is enough to do a fsck.ext3 to restore?