Any browser on iOS/iPadOS etc. is just a reskin of Safari. It might add new features - VPN, closing-all-tabs-feature, sync - but the underlying browser engine is still webkit, including all its limitations. Those limitations are, for example, limited debugging and no plugin support. Whereas I can install almost all desktop addons on my FF nightly on Android, I can't even have adblock on "Firefox" iOS. And even after Apple opened up the browser stuff, so FF can now be based on gecko, Mozilla would need to create and maintain a whole new App - for the EU, because other countries won't get those possibilities ever.

So FF on my iPad is just a way for me to access website-only stuff. In my Android phone, I also use eg. youtube/piped, deepl, maps in FF. That would be a pain on iOS due to missing Addons.