Yes, just walk over to the Mairie, show them your carte de legitimation, your proof of residence in Ferney Voltaire (utilities bills), and they will tell you what other documents you need to provide. It is very straightforward and painless.

Check with Human Resources at your place of employment about taxes. They probably reimburse you for any taxes you pay to the French government, but be aware that you will have to file tax returns (declaration d'impots) to France every year. France bases its taxes on residence, rather than where your income comes from or your citizenship. The UN and its agencies reimburse you for those taxes, but check with them what the administrative formalities are.

Dear JR M,

Thank you so much for your response.  I will definitely talk to HR guys.

Have a wonderful day,

Irina.