Suggest good free privacy , security based proxies that are compatible with firefox's foxy proxy .

I looked it up on DDG but couldn't find any defenitive answers . If you can put in the info that one would need to attach the proxy to foxy proxy and an ELI 5 would be much appreciated too . Thanks for the answers in advance . I know free services are bad just wanted to see if someone has any hidden gems like proton hosts free...