Nitrous oxide doesn't burn with oxygen, it acts as a strong oxidizer and may enhance combustion of something else. (plus it anesthetizes people and excessive exposure can kill).
It decomes into oxygen and nitrogen, and the resulting oxygen will enhance combustion. Quote from an MSDS on fire fighting"
http://www.camd.lsu.edu/msds/n/nitrous_oxide.htm
Fire Hazard Data
Flash point: n/a
Extinguishing Media: Oxidizing Agent. May accelerate combustion. Use media appropriate for surrounding fire. Use carbon dioxide, dry chemical powder or appropriate foam.
Special Fire-Fighting Procedures: Evacuate all personnel form danger area. Do not approach area without self-contained breathing apparatus and protective clothing. Immediately cool containers with water spray form maximum distance until cool then move containers away from fire area if without risk. If containers are leaking reduce vapors with water spray or fog. Shut off leak if without risk. Move containers away from fire area if without risk.
Unusual Hazards: Oxidizing agent. May accelerate combustion. Contact with flammable materials may cause fire or explosion. Container may rupture die to heat of fire. Decomposes explosively at high temperature. No part of a container should be subjected to a temperature higher than 52ºC. Vapors form from this product and may travel or be moved by air currents and ignited by pilot lights, other flames, smoking, sparks, heaters, electrical equipment, static discharges or other ignition sources at locations distant form product handling point. Most containers are provided with a pressure relief device designed to vent contents when they are exposed to elevated temperature.