Themes criticism

why are preview themes no longer animated in the browser when you move the cursor over them ?
and what are these strokes and dots in the thumbnail of the themes?

Not sure why the previews were removed, but you can now easily install and uninstall a theme directly from AMO, so you have to decide to click instead.

The previews show mock UI elements of the browser so you can see what the UI would look like with the theme applied.