But what if they don't need that many people working on Firefox? What if AI, VR, and Network programmers are fundamentally different in skills from a web browser programmer, and don't want to change their career trajectory?

Not every project makes 2x the money with 2x the people. It's the "Why can't 9 Mom's give birth in 1 month" problem. Hell most projects will slow down significantly with an influx like that.

Look, layoffs suck, but it's quid-pro-quo. Employees can leave at any time too. If a company isn't abusive or arbitrary with their layoff decisions, has decent layoff benefits, and doesn't refuse to give job recommendations, it's hard for me to hold it against the employer.