"Relay Premium is available in the United States, Germany, United Kingdom, Canada, Singapore, Malaysia, New Zealand, France, Belgium, Austria, Spain, Italy, Switzerland, Netherlands, and Ireland. " (https://relay.firefox.com/faq)
Note that that's for the Premium service - the free tier is available in most countries. We're hoping to expand to more countries in the future.
Edit: looking FAQ it appears it's not even available in Finland, I'm active user of relay and i saw the upgrade option, not reading the FAQ at all.