A long time ago, Mozilla did have the option to embed Gecko into apps. It was badly-documented and difficult to use.
A modern embeddable Gecko engine could be promoted as a modular, cross-platform alternative to Electron. The Gecko advantages: stripped-down, faster and less memory hungry than Electron (assuming these features can be achieved).
The traction that Electron has gained as a cross-platform option for building apps is huge and is only set to get bigger (whether for better or worse). And yet, Mozilla is completely absent from this space dominated by Chromium/Electron.
Imagine if thousands of developers place their trust in Mozilla because they have built their cross-platform apps using Gecko. They want to see Mozilla grow and succeed because they have a stake in seeing Gecko development succeed too. (And that could include large corporates sponsoring Mozilla to sustain development of Gecko.) Unfortunately, it is probably too late (or too unrealistic) for this to happen.
Would any of the above revive Firefox? Possibly not. However, an embeddable Gecko engine may give Mozilla new opportunities.
https://mykzilla.org/2017/03/08/positron-discontinued/
Revolving door management that has no clue what initiatives the previous management started and wants to start all their own initiatives really hurt Mozilla in the last 5 years.
However to my astonishment, these isn't even one Gecko-based alternative. I've found a few based on WebKit (I've ended up using Qt5 in Python), a few based on Chromium (including Electron / nwjs), but zero for Gecko...
If perhaps Gecko would be easily embedable (and perhaps used less resources than Chromium), it could start appearing in other applications, and thus at least get some market-share in that segment.
* Palemoon * Waterfox
You mean Facebook? No thanx.