An extension would allow me to use FF as I usually do for all sites except for list-of-blocked-sites-in-EU that the extension would work its magic on to allow data through. Also, I wouldn't have to look for a secure proxy myself and it would work (hopefully) on FF for mobile devices.
(Right now I'm using Tor which was already suggested in a different comment. The effort of having to open Tor is small but I was wondering whther an extension like Censor Tracker existed.)
I suppose a proxy could work. Ideally I would have multiple proxies working within the same profile like
Proxy 1 for websites A, B, C (uni proxy so I can access papers)
Proxy 2 for websites E, F, G (Russia proxy so I can read EU-blocked stuff)
I remember, “back in the days” there was an extension that scraped a list of open proxies by country and then used one of those proxies based on the URL. So what you described was/is possible. Nowadays I’m lazy and have nothing like this set up anymore.
There also is a problem with open proxies: They could be extremely slow or not working at all but being listed as fast and online so any type of automatism would select them.
You also never know who’s running them. If you host a proxy or VPN overseas and use this one you at least have some control over what it does. The speed might also be better.
I guess it just boils down to how much money you’re willing to pay.
The problem with Tor is, that it is very slow because how it works. You also have zero control over the exit node. It could be run by a malicious actor scraping all your data and sending back false information. Tor is good for poking though government firewalls but not for security, so careful when entering confidential or personal data.