Earlier quoted context omitted.
I was responsible for extension author outreach at Mozilla at the time. The anger was terrible. And justified.
You might have knowledge and connections: Do you see any hope for a fork of modern Firefox that start with just the tiniest stuff, maybe adding back a simple tab strip api to let Tree Style Tabs work properly again, that kind of stuff, then go on to put Mozilla out of business as soon as the economy allows it? I'm only halfway joking here, and only about putting Mozilla out of business.
Why bother with the overhead of a fork? Perhaps a team of volunteers could put together a good enough proposal to be accepted by the WebExtensions team.