As a developer, shit like "Automatic unpartitioning through heuristics" alone is enough that I won't touch this. Full stop.
Firefox is now breaking the contract I expected it to fulfill as the user's agent, and it's doing it fucking at random.
I happen to live in a space where I do need cross site support (both for cookies and requests) and frankly, between Google's push for SameSite, and now Firefox's selectively breaking the cookie jar, I'm pissed.
I'm a bit boggled that we haven't settled on a decent solution to let a site declare how it wants to interact with other sites.
This already fucking exists for mobile too, both Android and iOS support an opt-in manifest declared at a /.well-known/ path on the origin in question, why the fuck are the browser vendors so DEAD SET on removing control from the sites themselves in favor of these rushed, half assed, shoddy solutions.
Let me declare the sites I want to allow to share my resources. Let me do it at a known location, with a standard manifest, with finer grain control than "Random fucking heuristic" and "strict/lax/none".