I’ve just done a little bit of work on this – I took a copy of songs.db & manually edited it for a playlist where 2 tracks were missing because their titles included ISO-8859-1 legal accented chars.
1) Songs are in songs table, no problem there
2) In the playlist table I corrected the items to 10 from 8 for the specific playlist
3) I added two playlistitems table entries for the errant songs
I changed FF config to disable scanning, stopped FF, copied in the amended songs.db, restarted….
All worked – iTunes shows all the songs with the correct characters in the titles.
So.. where are the .m3u playlist files parsed into the database?