Simply scrobble watched YouTube videos into Last.fm with this extension. Automatic scrobbling takes place 4 minute after a music is played. You can also manually scrobble by pressing the count down text.
Using this extension you can also like or dislike songs without the need to open Last.fm
note that to prevent unwanted scrobbling, the extension pauses the count down when the song is paused. Also the scrobbling box plus the like button only appear if you are on Music or Entertainment categories.