Fire-Trolls are creatures that live within a volcano beneath the earth. A fissure opens that had allows them escape into the Ocean.
Aquaman tries to find ways to stop the trolls, who are attacking his home. The trolls attack an island where the Americans are keeping missile’s at a base, but even their weapons could not stop them. Aquaman figured out that intense cold might stop them; he goes to a mainland laboratory to find a chemical that can freeze the creatures.
The chemical doesn't work it just slows them down, the trolls then try to get rid of the stuff but is spilt onto Aquaman and Aqualad, who are frozen. Quisp an extra dimensional ally sends a beam energy at them that shrinks them. They are tiny and need to get to water. Aquaman tricks a pelican into dropping water on them. Then they continue back to the ocean. The shrinking effect was only temporary as they are grow bigger with each step
They meet up with Quisp who tells them trolls took all the missiles. The trolls plan to use the explosives destroy the volcanoes and become the masters of the planet. Aquaman sends Quisp to distract the Trolls by leading them back to the island. Once there he covers them with freeze solution again and Quisp use repelling ray to shrink them. They them take the trolls back to the fissure and attempt to close it for good.
The New 52
In the New 52, in Aquaman #38 the re-imagined Fire Trolls appear. They protect a passage to the Atlantean dimension of Pacifica. They have similar abilities with their pre New 52 selves. In Aquaman #39 it is revealed that they live in a volcano and serve Karaku, the Volcano God.