It comes down to the high-level architecture of Gecko. Gecko is not just a web engine; it is in many ways an entire application framework. Gecko inverts control such that it implements the entire main event loop of the application. Desktop Firefox is essentially one big privileged HTML+JS…

It had to be rewritten. Essentially there was no formal interface between the frontend and Gecko, and it had turned into a sluggish hairball of a monolith. We redesigned Gecko on Android to be embeddable (GeckoView[1]) and so a new frontend had to be written. That part was absolutely necessary. The…

> It's sad that Firefox engine is so difficult to embed and we could have seen more projects using it. Not on Android, it isn't. https://geckoview.dev

(Former Mozilla developer here, who worked on GeckoView[1], the modern way to embed Gecko into Android apps, including all currently shipped Mozilla browsers on Android) From an engineering perspective, the sad thing about this is that the work to finish extensions in GeckoView was essentially…

> This is only due to the failure (and unwillingness) of Mozilla to build a truly modular, expandable browser. Not on Android: https://geckoview.dev

That’s essentially because the leg work hasn’t been done to make it embeddable on most platforms, with the exception of Android (https://GeckoView.dev)

Not quite. It can be used when any app calls the Android custom tab API. It is not a drop in replacement for Android's Webview. See https://geckoview.dev