Stop After Track for Google Music
Just click in the "Now Playing" menu next to the song title and click the button! The music will automatically pause when you reach the end of the current song. This extension requires turning on HTML5 audio from the Music Labs page. This an an open source extension. See https://github.com/Glench/Unofficial-Google-Music-Stop-After-Track Note that detecting when the song is ended is kind of janky, so it may not work perfectly.