[peter-m80]

The ico file format allows multiple resolution icons, so a lot of data

[weetii]

Good point, I might add a section in the article where I list alternative approaches. Thanks

[dodslaser]

Or just put the entire website in a <foreignObject> and render it in the favicon.

[econ]

You can use any image format. Try using an animated gif.

I don't know what this is but it's huge.

https://news.ycombinator.com/favicon.ico