Outside the 12nm territorial limit no international organisation, such as ICAO, or national government, is entitled to prevent free passage by sea, or air, except in so far as they wish to do so by force of arms. FIRs are only applicable to assenting parties.
An FIR is established in order to provide a flight information and alerting service. FIRs can and do extend into international airspace. However, within each countries FIR there are rules and regulations for flying your aircraft, whether it's a private or commercial flight, a civil or military irrespective of international airspace.
Each FIR is subdivided into classes of airspace. These classes of airspace have specific rules. A lot of this airspace requires the pilot to communicate with ATC and follow ATC instruction. If you don't do this then there are penalties for non compliance. One of these is finding a Typhoon, fully armed, sitting on your wing!
Most countries allow free passage of their FIRs/airspace under the Chicago Convention providing you follow the rules. Them TU 95s did not follow the rules.