in the beginning, this extension was great. Lately it's creating duplicates for different audio tracks from different YT vids. Their homepage doesn't have a bug track. What a bummer!

atencioso

This addon simply converts to mp3. Works well.

Conversion is very fast and simple to convert to MP3. Much more efficient than larger programs.

Well done. Converts fast and many files at once at whichever bit rate you want.