FIR means Fairways in regulation. Basically, did you hit your ball onto the fairway with your first shot. They don't officially use that stat anymore though, they use "shots gained: Tee-to-green" now, which combines FIR with GIR (greens in regulation). I'm not 100% sure of how they calculate it, though. Hope this helped!
If you want to learn more, it's probably easier to just find a website that answers all such questions in one place, like this one.
You might mean: 'fore - meaning 'Watch out afore' or ahead!