(3) Chrome is migrating to using it's own store: "Historically, Chrome has integrated with the Root Store provided by the platform on which it is running. Chrome is in the process of transitioning certificate verification to use a common implementation on all platforms where it's under application control, namely Android, Chrome OS, Linux, Windows, and macOS. Apple policies prevent the Chrome Root Store and verifier from being used on Chrome for iOS."
(1) Firefox already uses its own root store
(2) App developers can include additional roots in addition to the system root store: https://developer.android.com/training/articles/security-con...
(3) Chrome is migrating to using it's own store: "Historically, Chrome has integrated with the Root Store provided by the platform on which it is running. Chrome is in the process of transitioning certificate verification to use a common implementation on all platforms where it's under application control, namely Android, Chrome OS, Linux, Windows, and macOS. Apple policies prevent the Chrome Root Store and verifier from being used on Chrome for iOS."
https://www.chromium.org/Home/chromium-security/root-ca-poli...