Mina Ashiro vs Firestorm (Pre-Crisis): who would win?

Mina Ashiro favored — Slight edge (~55%)

Mina Ashiro · Kaiju No. 8 · Base

Tier
HIGH 6-B, up to HIGH 6-A
Attack Potency
Large Country Level, up to Multi-Continent Level
Speed
High Hypersonic, up to Ftl
Durability
Mountain Level+, up to Large Country Level

Firestorm (Pre-Crisis) · DC · Base

Tier
HIGH 6-B
Attack Potency
Large Country Level
Speed
Supersonic, up to Massively Ftl+
Durability
City Level

A heuristic estimate from normalized VS Battles Wiki stats: tier, attack potency, speed and durability.