Privacy and ethics around proprietary software, while obviously related (in that open software is obviously more transparent), are largely orthogonal. You can have closed/proprietary software that respects privacy (Apple), and you can have open software that doesn't (Chrome).

This just smells of whataboutism.

As for your hypothesis that websites will start blocking browsers that ban tracking and so forth, frankly, that remains to be seen, and my bet is we'd never actually see that happen in practice. The optics are just too toxic. Surveillance capitalism survives because people don't know it's happening. Banning a browser like Firefox would call attention to an infrastructure and ecosystem that those individuals don't want to talk about in public.

Edit: As an aside, if sites did start banning privacy-conscious browsers like Firefox, I'd just stop going to those sites. In that respect, I'd actually perversely appreciate something like this: It'd finally make it blatantly obvious who is and isn't collecting and profiting from data about me and my actions online without my permission.