What did they do? I don't notice anything different.

Smooth scrolling but that interferes with my scroll rate and vimium which also optionally does smooth scrolling.

Generally, web designers really shouldn't touch scroll behavior at all, it's rather bad practice.

I noticed this and was instantly aggravated by it (it's especially obvious on a Mac because it doesn't do the "rubber-band" bounce at the top and bottom). What purpose does it even serve on this page?