Firefox isn't a transitive dependency on the desktop. If an app uses a WebView[0] control on Windows, Firefox has no effect on its behavior and performance. It uses the Edge engine to power WebViews. On iOS WKWebView currently uses WebKit.
The EU apparently wants to change this behavior on iOS. A WKWebView would be backed by the system's default browser selection if it made claim to support WKWebKit views. So your third party app with no direct connection to Firefox that uses a WKWebKit view now depends on Firefox handling the loaded pages in the view. If they don't work in Firefox or whatever browser the user has selected the third party app is affected by the choice of browser. This also has an affect on web apps on the Home Screen.
The issue with Chrome is it already dominates the web. App vendors will drop Safari WebKit support as soon as WKWebKit no longer mandates the site work in Safari WebKit. Without iOS enforcing support for Safari WebKit by being the only option for the non-trivial number of iOS users of the web, Chrome will be the only supported browser in apps and the wider web.
...apps don't use WebViews on Windows (or MacOS really, for that matter) because they are unstable APIs that Microsoft and Apple both break in nonsensical ways. It's why Electron is king, in many respects. The only desktop software that use WebViews afaik are the "native apps" which really ought to be handled with a leaner library anyways.
> App vendors will drop Safari WebKit support as soon as WKWebKit no longer mandates the site work in Safari WebKit.
The EU apparently wants to change this behavior on iOS. A WKWebView would be backed by the system's default browser selection if it made claim to support WKWebKit views. So your third party app with no direct connection to Firefox that uses a WKWebKit view now depends on Firefox handling the loaded pages in the view. If they don't work in Firefox or whatever browser the user has selected the third party app is affected by the choice of browser. This also has an affect on web apps on the Home Screen.
The issue with Chrome is it already dominates the web. App vendors will drop Safari WebKit support as soon as WKWebKit no longer mandates the site work in Safari WebKit. Without iOS enforcing support for Safari WebKit by being the only option for the non-trivial number of iOS users of the web, Chrome will be the only supported browser in apps and the wider web.
[0] https://learn.microsoft.com/en-us/microsoft-edge/webview2/?f...