Control Freak Script for adding "hide" button to YouTube. So you can listening to music without looking like you are watching music videos.

youtube_hide_button.js

// add libs 
// http://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js
// https://raw.githubusercontent.com/hazzik/livequery/master/dist/jquery.livequery.min.js

$("#upload-btn").livequery(function(){

  $("<button id='hide-btn'>Hide</button>").insertAfter("#upload-btn");
  
  $('#hide-btn').click(function(){
    if ( $('video').css('visibility') == 'hidden' )
      $('video').css('visibility','visible');
    else
      $('video').css('visibility','hidden');
  });
});