Animated themes not working on my browser

Can anyone give me some troubleshooting steps. Animated themes will work when I’m previewing them, but after I download them they don’t work. Does anyone else experience this? What should I do to get them to animate?

Firefox hasn’t supported animated themes for a while. What happens is that the theme will work initially, but when it’s installed Firefox will crop the image (for performance reasons). This breaks the animation in animated themes.