I am using a socks4 public proxy for more speed/bandwidth. I am currently using it for downloading files. Now I want to use it for social media or daily day usage. I know that they will get all my traffic. I use DNS over HTTPS in Firefox. So, I think that they won't be able to redirect a phishing site or something like that. But, what about other things like, my password? I also enabled HTTPS mode in Firefox. So, can I use it safely for daily usage?
As long as you are using TLS (HTTPS), you will be safe from tampering and sniffing. But beware that it could read and tamper with data from any site that does not use properly-configured TLS. The proxy will also be able to see what sites you visit and for how long, but won't be able to view what you send.
For the purpose of evading censorship and simple throttling, you could also use an encrypted VPN.