Mozilla cannot be unplugged on demand. That would cause Google to become a monopoly, and they would be held to extreme harsh laws by the EU. Like in the case of IE6 back in the day.

Google does not want that, so they donate to Mozilla to keep Firefox as a competitor. And Firefox has to do jack shit in return other than exist.

The only way Firefox could be unplugged is if a new non-chromium browser becomes one of the big browsers.