Sure, Amazon doesn't want hundreds of extra lawsuits, but the staff also don't want to waste their money on legal fees for a suit that's a guaranteed loss. Case law is very well-established.
What's with the assumption that it's the law that is keeping Amazon from mass-firing staff who won't come in?
The approach they're taking is just a smart business decision. It allows them to spread the disruptions out so they're more manageable, to keep employees who's skills justify flexibility in the WFH rules, and prevents the PR impact of a mass termination.
I've read that the main reason Google funds Mozilla is to prevent a monopoly situation. I bet they'll stay committed.
Mozilla really does need to diversify their funding though.