Wait for it; there will be mandated software on 1st-world machines in our lifetimes. Root on your machine is already a bit of a fiction because of government action (the cpu management engine); look for that to become more explicit after the first really big blackout/other catastrophe caused by a computer security failure.
Unrestricted mathematics are too dangerous to be allowed to normal people.
They won’t mandate a specific browser, but they can regulate functionality.
Piracy is already considered theft. Viewing webpages without ads is basically “stealing” web content. I would not be surprised in the slightest if some big advertiser runs with this idea and lobbies for strict legislation. And they likely would succeed, quite honestly. Congress doesn’t understand adblocking or the internet, but they have a vague idea of digital piracy.
IANAL, but I highly doubt that the government will mandate what browsers people run on their computers. Outside of North Korea, of course.