Definitely not invincible, I think one would be stuck with chromium forks and manifest v3 if security and privacy are key. There is really no silver bullet :(

Edit: Anyone down voting this doesn't understand browser tech. Chromium is years ahead in security, and various forks take privacy seriously. And since Gecko has security concerns, Chromium is actually more relevant for those issues. I use Gecko shit for everything I can, but if you're going to pretend there is a lack of privacy just for using Chromium, you're admitting ignorance and probably only know about Chrome.