YouTube videos auto-starting was a pain for me, the site is SO less annoying now, yet the developer was wise enough to give the option to not pause videos in playlists because they are (at least for me) used differently. Other great options I use are the mousewheel for volume control and disabling autoplay and annotations. Makes YouTube SO much better for me. Has an adlbocker but I use uBlock Origin and Ghostery so I don't enable it.