Theoretically they could still focus on developing a privacy-first browser on top of the core engine, and continue to influence web standards by implementing them as plugins with some glue patches maintained as a running fork on top of the Chromium code. As it is now, the fact that Firefox uses Quantum instead of Blink and SpiderMonkey instead of V8 isn't really a differentiator for the vast majority of users. There's a vague sense that a technology monoculture is unhealthy, but I would argue that the real threat is a browser monoculture, and Mozilla apparently can't stop that from happening with their current strategy because Firefox is losing.