On its face, it's a tough sustainability position for an org of Mozilla's size b/c browser revenue - today - is from controlling the search bar (and maybe now payments APIs?). By making Firefox embeddable, Mozilla gives that revenue to whoever is doing the embedding. Ex: Brave <> Chrome engine.
Building for embedding developers can be super distracting if no sustainability, which isn't a problem for Google: They still make money from embedding by owning the embedding environments like Android. AFAICT, Mozilla failed to land in sizeable markets there. They tried to own & partner in the embedding envs -- e.g., FirefoxOS -- so maybe the trick is to get a more generous rev share for phone vendors wanting to break free of Google? Historically didn't seem to really work out, but maybe genAI w/ consumer/prosumer-grade UIs is reopening that door.
Evolutions like that in turn may take quite an engineering & culture rethink as well, not easy to turn such a big & decentralized ship. I'll keep rooting for them!
I’m not well-versed on the internals of FirefoxOS, but I’m not sure it really counts as embedding because to my understanding, the entirety of the user-facing UI was built with Gecko. Embedding entails usage of the engine with unrelated toolkits, e.g. AppKit/UIKit or GTK.
If that’s true, then Mozilla wouldn’t have been making money from Gecko’s ability to embed with FirefoxOS unless the project took a sharp corner and changed UI toolkits.
The FirefoxOS scenario would be Gecko embedding in FirefoxOS, so Mozilla is their own customer, and makes $ by being the controller of FirefoxOS - OS search, and configuration of browser search
It's less likely the handset manufacturer would be able to change search bar defaults in those scenarios, at least without a stronger profit sharing negotiation, as they'd probably be already negotiating a more careful licensing & teaming agreement
There is only one browser, because browsers need to be embeddable, and Firefox isn't.