I honestly don't know. Maybe if you did it on your phone or iPad, but I'd think that it would default to the domain of the email address under which the Netflix account is registered. If it's a US account, etc etc. That said, you can get physical discs fairly inexpensively if you want to go that route. You could just purchase the series in HD on Amazon for $7:
Vudu and Amazon also have the season at $5 right now on their digital services. Pick your favorite 'verse for your purchase.
https://www.vudu.com/content/movies/details/Firefly-Season-1/129456
The last time I sat down to watch a whole series was Firefly and I bought it streaming for $13 https://www.amazon.com/Serenity/dp/B000H4TX9I/ref=sr_1_5?ie=UTF8&qid=1506115712&sr=8-5&keywords=firefly