Let me explain what Better Youtube does. As I said earlier it’s basically a collection of Greasemonkey scripts that add various features to Youtube. You can enable and disable those features in the options of the add-on which is accessible  in the Tools > Add-ons menu by clicking on the Options button next to the Better Youtube extension.

The main new feature that has been updated just recently is support for high quality Youtube videos which will be automatically loaded if available. No need to fiddle around with url strings anymore.

Five options are available when you click on the options button. You can add download links to each Youtube video which makes it possible to download them, use an alternate player, hide comments, show full video descriptions by default and enable Theater View.

If you enable the latter all other options become unavailable. Theater mode is very nice if you happen to view high resolution, or higher resolution, videos at Youtube effectively doubling the size of the video.