Listening YouTube audio without any tab
This extension is no more support.
Pleas see: http://shinychang.net/article/52fa2d618ec287c1055a3c8d
If you want a better extension, I suggest streamus.
Official website: http://streamus.com
This player can play the youtube video in background.
This player is based on HTML5 player, may have some issue.
If you have any problem, please let me know.