It is a standard, unmodified Pokemon Fire Red (U) ROM. The squirrels tag is purely cosmetic. The game boots normally, Professor Oak introduces himself, you pick Charmander/Bulbasaur/Squirtle, and everything runs as expected. The only anomaly is that the filename has no impact on the gameplay.
Happy hunting, trainer. And watch out for those squirrels. 1636 - Pokemon Fire Red -u--squirrels-.gba
So the next time you see --squirrels-- in a filename, don’t delete it immediately. Open it. Play it. Maybe—just maybe—there’s a secret message hidden in Viridian Forest, written in the bark of a digital tree, waiting for someone to find it. It is a standard, unmodified Pokemon Fire Red (U) ROM