Result
  1. Build nspire-emus/firebird on GitHub by Qt for iOS on a Mac computer, OR Download the built ipa (asia.turx.firebird-emu, if you trust me);

2. Install AltStore and log into any Apple account (do not need to be in the paid Apple Developer Program);

3. Open firebird.ipa by AltStore;

4. While keeping the connection to the same WiFi network as the computer from which AltStore was installed, Firebird will be automatically installed;

NOTE: The app will be automatically renewed when the iOS device is connected to the same network as the computer mentioned above

5. Use Finder or iTunes to copy necessary images to firebird;

6. Configure as on Android;

7. You are all set!