edit: seems to be a bug in Firefox, not FoxyProxy, other proxy extensions have the same issue. glad for a prompt response from developer

When a SOCKS5 proxy is enabled, if DNS over HTTPS in Firefox is turned on, Firefox does not seem to respect if the proxy server handles DNS or not; it will still query DNS through Cloudflare or NextDNS or whatever it's set to in the browser settings, potentially leaking DNS information