It works on HTML5 video. So be sure to set your preference for video formats at youtube.com/html5.

YouTube recently (Dec 2014) decided to take away the auto-play toggle on playlists and made all playlists automatically go to the next video in the list after a video ends.

This is a simple script to pause a video when it reaches one second remaining in the video if you're on a playlist page. (If you would like all videos to pause at one second, change the @include to be just *.youtube.*)