Automatically pause YouTube HTML5 videos on Youtube
This script will automatically pause videos on Youtube. Works with the HTML5 video player that has been updated in August 2015. This only works on video pages that you open in new tabs or windows, directly navigating (i.e. left clicking) won't automatically pause the video.
This script works based on MutationObservers that will recognize when the video has loaded and the play/pause button is available. This means that on slow computers (or when opening a lot of tabs at once) this will likely play a few seconds of the video, but it will pause them more reliably than other more simple methods.
