The browser I use does not process Javascript or CSS. I therefore have to do nothing. :)
However, I would guess switching browsers is extremely unlikely for a great number of users. Google must know that. That is why they can do something like FLoC. They must know that not many users are going to switch browsers.
I was not suggesting it would be users who set up the proxy. On the contrary I was suggesting we might see someone set up a proxy to help users who are unable/unwilling to help themselves. There are so many simple things I do for myself that I see being set up as "SaaS"-type projects/businesses and then posted/discussed on HN.
However, I would guess switching browsers is extremely unlikely for a great number of users. Google must know that. That is why they can do something like FLoC. They must know that not many users are going to switch browsers.