Spending time on Firefox OS honestly would have been a productive use case and it'd probably also be a decent revenue source for Mozilla rather than abandoning it and letting KaiOS pick it up.
Especially given that it's now become the third largest mobile OS with over 100 million active users worldwide.
And not just a focus on Tech but also focus on product. i.e Firefox.
You could have them focus on Tech and they spend all their resources on Firefox OS.