Animating background-position can be expensive, especially across the whole screen. I had a situation last year where a fullscreen snowfall (animating background-position like this) caused an annoying white flicker in Firefox. You might want to read this article and experiment with converting it to animating transforms instead (less expensive). http://blog.fofwebdesign.co.uk/37-css-animations-performance-gone-bad-and-how-to-fix-it
Caveat: This was for digital signage and so wasn’t tested across all browsers or devices, other that the few it displayed on.
It also depends on what else is going on in your page.