So far I have not been able to figure out how to use MusicBrainz as the default tag source (under Tools, Options, Tag Sources). MusicBrainz.src shows up in %APPDATA%\Mp3tag\data\sources, but I'm unclear what to do next. freedb is the only source that shows up under Tag Sources. Help would be appreciated. Thanks.
There is not much to configure about other tag sources.
You simply select them in the menu Tag Sources.
If you need more tag source scripts, see the forum section on tag sources
and move a downloaded script to the MP3tag
data\sources folder before you start MP3tag.