Gecko/Webview is a compile-time switch and both the F-Droid and Play Store builds use Webview. The iOS version is Webview-only or Apple wouldn't allow it on the App store.

I think you meant WebKit for the iOS version?

Oh, it uses Webkit? Huh

Required for iOS or Apple won't allow it on the store.

Why hasn't the EU charged Apple for abusing the monopoly position? Didn't they do that to Microsoft, or has Apple sweetened them up in some other way?

Technically, Apple does not have a monopoly, unless you want to argue they are the monopolist of the market for iOS devices. They don't even have a majority market share of smartphones in most jurisdictions. That being said, I still believe it is an abuse of market position, and I'm not sure how we can fight it.

In most parts of the EU Apple has a marketshare around or below 15%. That’s about the same that Windows Phone 7 had at its peak.

So, think about how much of a monopoly position Windows Phone 7 had, and try to imagine Apple had that. You can probably imagine why Apple is not in any shape to abuse their position.