I bought this halotron fire extinguisher for my Firebird -
https://www.amazon.com/gp/product/B001ECQ5NE/It was a little cheaper last year when I purchased it, around $110. If you go with a dry chemical extinguisher and use it in the engine bay, you risk getting the dry powder inside your engine which can completely ruin it. I figured it's worth spending a little more just for this reason.
The mounting location choices in the cockpit are either going to be front passenger footwell, rear passenger footwell, or on top of the center rear transmission tunnel. Since I didn't want to drill holes in the tunnel and didn't want to see it continuously in the front, I opted for the rear passenger footwell. I don't plan on carrying rear seat passengers so this was the best location for me.
I fabricated a U-shaped bracket that mounts to the seat bolts. The extinguisher came with a quick release holder, which I bolted to my bracket, so didn't have to purchase a separate one. You can see the results in the photo below.