An edit of http://freestyler.ws/style/91240/listen-on-repeat-dark-negativ. This has some fixes for the new site layout.

PSA:

YouTube now has a "loop" feature that is built into the HTML5 player. As the name suggests, it allows one to toggle looping on and off. All that you have to do to activate it is right-click the player and click the "Loop" button (as explained https://productforums.google.com/forum/?hl=en#!topic/youtube/T3R3sCmrkLI;context-place=topicsearchin/youtube/loop). So, Listen on Repeat is no longer needed and I have since stopped using it in favor of the built-in functionality. You can find more info about the HTML5 player at https://www.youtube.com/html5. Also, if you want a dark YouTube theme, here's a rather good one (which I use): http://freestyler.ws/style/55584/black-youtube-by-panos.