I’ve actually noticed similar quirks when testing sideloaded apps that use external web-based components on iOS.
From what I understand, all iOS browsers — including Firefox and Chrome — are still required to use Apple’s WebKit engine under the hood, so in theory, rendering should be pretty consistent across the board. But in practice, Firefox on iOS sometimes does behave differently, especially when it comes to embedded views and redirect handling.
I’ve run into issues with OAuth flows not completing properly when a sideloaded app opens them via Firefox instead of Safari. It seems like Firefox doesn’t always handle certain cookies or session storage correctly in those contexts — especially when jumping between in-app browsers and external tabs. My guess is that it's partly due to how tightly Apple locks down app-to-app communication and how limited browser extensions or advanced networking are on iOS.
One workaround that helped me: try forcing the app to open links in Safari rather than relying on Firefox’s in-app webview. You can sometimes tweak that using settings in the sideloading tool (AltStore, Scarlet, etc.) or by modifying the app’s Info.plist before signing.
If you're exploring sideloading tools, the Scarlet iOS App Store is definitely worth a look. It provides a smoother UI and better support for advanced features compared to some alternatives. You can learn more at scarletapps.com.
