Firefleas can be easily killed, especially since they fly slowly, but it’s best to avoid contact or refrain from shooting all of them in the room; otherwise, Samus will be completely left in the dark. It’s still possible to see faint forms in the room if only a few Firefleas are extinguished, but it makes safe traversal and exploration more difficult.
Surprisingly, the Grapple Beam is completely ineffective against Firefleas.