> They hi-jacked the browser's `/` key to focus the field, which is something I hate.

You're not the first one to point it out. Please join github.com/mdn/yari to raise your voice. It's an Open Source project after all.

> They should have just had the search field focused automatically

Why? There's a lot of JS to load to make that work. If you never need to do a search (e.g. from a Google search) it would be a potential waste.

> Also, I'm confused, I thought https://mdn.dev/ was the new thing because Mozilla was stepping back from MDN. Is it a fork?

That domain is just an alias we don't currently use. It's still the old MDN from Mozilla. No fork.