Firefox
- Install the extension Cloud Firewall and configure it to block Cloudflare (and/or other large content providers such as Facebook and Amazon)
- In Mozilla Firefox 70 and above, Mozilla enabled DoH (DNS over HTTPS) with Cloudflare as default and only DoH provider. Rationale [1]. Set network.trr.mode to 5 in about:config now to disable this in the future.
[1] While DoH has its advantages and disadvantages, and DoH can help mitigate MITM attacks on insecure networks, it is also potentially dangerous to centralize DNS towards one powerful company.