They really can't, though. There's a pile of corpses of people who tried to embed Gecko, because it turns out Netscape/Mozilla is really bad at keeping a stable ABI. I doubt anybody remembers K-meleon anymore, for example. As far as I know Servo was supposed to be the new, embeddable engine, but that's mostly cancelled now and the Rust bits are just being rolled into Gecko (via Project Quantum).
I believe that's why Webkit was based on KHTML… the Mozilla developers Apple hired realized that had a better chance of working.
Maybe Mozilla has changed since all that happened and they're more friendly to embedders now? I've been out of the loop for a few years at this point. I don't think I've heard anything though, and they've built up a reputation…
Well, they are not embedding Blink to build a new browser either - they just fork Chrome. They could have forked Firefox the same way and customize it to their liking.
But that would not have solve their web compatibility issue in such an easy way.
Yes. GeckoView is Android-only. GeckoView is currently used in Firefox Focus, Firefox Reality VR, the upcoming "Fenix" browser, some Mozilla test apps, and a couple third-party apps.
I believe that's why Webkit was based on KHTML… the Mozilla developers Apple hired realized that had a better chance of working.
Maybe Mozilla has changed since all that happened and they're more friendly to embedders now? I've been out of the loop for a few years at this point. I don't think I've heard anything though, and they've built up a reputation…