Normally when you click a video on a YouTube playlist page, the video plays in the context of the playlist, meaning the next video will play automatically when the current video ends.
Playlist Abandoner is a Safari/Chrome extension which adds a button to each video on a playlist page. Clicking that button will open the video on the normal watch page, outside the context of the playlist.
The Chrome version of the extension is available on the Chrome webstore.
To install in Safari, download the
.safariextz file from the latest release
and double-click it. Safari will ask if you trust the extension before installing.