Assuming that the D: drive you mention is on the same machine, is the playlist folder and the folder for the files that they point to set up in the Firefly configuration options? Is the switch for processing .m3u files as playlists set to yes? And is Firefly scanning so that it picks up new files? Once every 10 minutes or so works well for me. Basic questions, but I know from my experience with Firefly that these are easy to miss when trying out new ideas.
FireFly Media ServerThe original FireFly Media Server