I run Firefox myself, but you can't really blame developers for not wanting to deal with the whims of Mozilla.

I am looking for info. Why is Firefox web engine no the go to choice for foss projects? It is not embeddable or just really complicated or or what? If so are they making any progress towards more adoption?

Mozilla is not very developer friendly. Gecko uses a two decade old method of RPC, the lib interface (XPCOM based on Microsoft's COM) is about the same age, the documentation hasn't been updated in a decade even though the code evolved, and I've heard from 2 employees directly that it's not important to them.

It's not really a surprise that gecko isn't the primary choice for browser developers.

After briefly looking into this, my understanding is that the embedding documentation hasn't been updated in a very long time, and the overall architecture doesn't lend itself to embedding.

I think it'd be cool to merge it (this) with the rendering part of netsurf, which can run on a framebuffer.