Update 2.1.2: Fix userscript conflict with Youtube CenterUpdate 2.1.1: Fix userscript conflict with Youtube+Update 2.0.0: This script now works on both Classic and Modern Youtube!

Note: Doesn't work with Modern Youtube (yet)! (Script to automatically restore classic youtube)

If you also want to be able to create a queue with videos to play after your current video has finished, you can use Youtube Play Next Queue.