db_sqlite3_open: Misc SQL Error: unable to open database file (/usr/var/cache/mt-daapd/songs3.db)
Have you thought of any causes for this problem?
My first guess would be permission problems.
Check which user runs firefly, and if it has read (and write!) access to the file.
Edit: OK, my bad. I see you used sudo so it’s root. Another possibility is that the database got corrupted. (it happens).
Delete it, and restart firefly. It will create a new database from scratch.