To restore animated thumbnail previews. Requires inline video previews to be disabled in your YouTube user settings (Go to https://www.youtube.com/account_playback and set "video previews" to disabled). Not Greasemonkey compatible. v5 Add new method for getting an_webp GIF-style thumbs when not available in YT's new homepage UI or subscription page UI.
Great, because I was sick of Youtube's thumbnail shenanigans and the crappy captions slapped over the thumbnail.