They don't get donations from Google, but get paid to include Google as the default search engine, right?

No important difference though. Mozilla tried to switch to Yahoo a few years back and backpedaled. In terms of what users expect, they don't have a lot of options. Google OTOH could do without the users Firefox has left. And I've personally observed Google strong arm "partners". Not sure I see a conspiracy here, but I'm pretty sure that if Google asks for concessions, Mozilla will see what they can do.