Originally posted by carver9
He senses Superman energy and either drains him or just blast him with red solar energy and yes, Red solar energy and kryptonite is a common weakness of Superman.
Scans of Firelord draining anyone - then scans of him doing it quickly enough to someone who has superspeed.
Scans of him producing red solar radiation.
Scans of him knowing what Kryptonite is, and how to replicate the exact wavelength.
Then scans of Firelord having the combat reflexes to know and do all this at speed before Superman punches him, and yes punches being a common weakness of Firelord.