Hardware firewalls provide some protection against the kinds of threats XP faces. More to answer your question; I'm running the latest available versions of Windows 10. I sometimes use FF 56 for its consistency in behavior, XPI addon support (NoScript and uBlock still function), customizable UI, and for critical tasks (banking (affected by the Cloudflare problem)). I use FF 90+ for daily driving, and I despise it.

Because machine is connected but didn't use internet.

It's for accounting purposes only - making invoices. Probably for one month it's used for hour or two max.

How is Cloudflare DDOS protection in your internal networks that them not supporting that version of XP is a problem?

For me - isn't problem. Because as i said machine isn't used for browsing.

To be honest i have friend of mine that have small furniture manufacturing. They have CNC machine with Windows98.