How would they loose? Right now people looking for a "component" are just using chrome(ium), so Mozilla does not have those "users" to begin with.
If Gecko would be as usable for integration as Blink is more people would use it overall which is a net benefit for Gecko.
Their loss lies in the fact that this would enable people to build competitors to firefox, as they would basically make a box of components to do exactly that.
Yet Firefox, the product, is what brings in money. Not the underlying tech.