Facebook has quite a few offices in Europe. However most are probably just selling ads and doing localization.
Dublin, Ireland; Hamburg, Germany; London, UK; Madrid, Spain; Milan, Italy; Paris, France; Stockholm, Sweden
Dublin, Ireland; Hamburg, Germany; London, UK; Madrid, Spain; Milan, Italy; Paris, France; Stockholm, Sweden
"Just?" That's their whole business. If they're selling ads in a country, then they're "doing business" in that country.