Suffice to say that we all deserve better.
Yes, I am quite aware of the contributions they also make to those platforms, but at lease those can be forked from, that ain't happening with what Google/Apple/Microsoft are selling as mainstream OSes.
For one, Mozilla is still a US entity. As an EU citizen, I'd rather have my taxes go towards funding EU entities, especially in this climate. And I'd rather have that EU entity fork Chromium, starting to contribute to its development, as that would be a wiser bet.
And also, governments funding projects such as Firefox is a bad idea because the citizens of those governments come first. As one example, many online BBC shows are geo-blocked in my country. The EU is meant to serve its citizens, not the world, and you don't want the open Internet to depend on whom people vote for in the following election cycle.
The only way to fund a project that has global reach is via a sustainable business model, not taxes.
You have to analyze a project, and that might mean you need to fork it. It all depends on how much you need to steer and help. If a community is happy to welcome some formal stewardship, then that might work too. There is a company that contributes a lot to Libre Office. The same with Blender, where there can be cooperative development.
A hard fork is always possible, and nothing bad if the vision and needs differ from teams. Some might fork the EU stuff in turn. The free software model is designed to support that.