Fire extinguishers stop a fire by removing heat, air, fuel. Any type of them wouldn't work becuase
Air: Flare could move out the way at any time, and I doubt you'll cover him entirely.
heat: It may work up until angry, where it's not as hot. At angry and above, you'll probably not because of how hot it is.
Fuel: Embros are Embros because of their core, which is basically their fuel source, and you're NOT taking that out any time soon.