YouTube: thumbnail previews

This script shows available thumbnails of YouTube videos and streams under the video. The thumbnail previews are clickable, linking directly to the images.

This script is not intended to be used all the time. Instead, just turn it on in your userscript manager whenever you need access to the thumbnails.

Example screenshots are from videos:

What is Kdenlive? The highest resolution thumbnail is on the left hand side, it links to https://i.ytimg.com/vi/g2Q6sluqc2I/maxresdefault.jpg
Me at the zoo – one of the oldest videos on YouTube, only medium quality thumbnails (right hand side) are available – https://i.ytimg.com/vi/jNQXAC9IVRw/mqdefault.jpg
the most important material in science – shows a bunch of different thumbnails: the custom one uploaded by the user and three from the video: one, two, three.

When a thumbnail of a particular resolution/quality isn't available, the default YouTube placeholder is used