Ask HN: Add falling snowflakes without slowing down page?

I'm looking to add a falling snow effect to a few of my sites for a week or two this December. (probably with "Let it Snow!" button to start the effect).

Most of the examples and tutorials I can find are pretty dated, very sluggish, and can lock up the page/browser, especially with a lot of tabs open.

What's the best performing way to add simple snow falling animations without significantly affecting page performance? (CSS3 Animations maybe?)

Also, is there a way to do it that is accessible, ie, doesn't trigger seizures as indicated in this article I came across?

http://wptavern.com/warning-wordpress-coms-falling-snow-feature-can-make-your-site-inaccessible

I feel like leaving making it opt-in (by providing a button) would take take care of the issue. There's something nice about being pleasantly surprised by the snow effect when browsing that's appealing, but not if it's going to trigger seizures >_<

I also realize that not everyone would welcome falling snow, so perhaps opt-in really is the only way to go.

Thanks HN!