Firenewts are a mostly forgotten race of humanoid salamanders from the worlds of Dungeons & Dragons. Cursed with a bizarre biology that limits them to areas that are simultaneously hot and wet - such as thermal springs - in order to reproduce, firenewts have attempted to compensate for this through aggression and religious fanaticism; they are invariably portrayed as a theocracy dedicated to either Imix or to other malign/destructive fire gods, such as Pyremius or Kossuth. As such, they frequently practice slavery and anthropophagy.
They are sometimes believed to be related to lizardfolk, but information on this vacillates.
Where you find firenewts, you invariably find Giant Striders; creatures that are either Ornithomimids (ostrich-like dinosaurs) or mutant scaly flightless birds that spit fireballs and which the firenewts raise as prized steeds.
For AD&D 2e, firenewts didn't appear until 8 years later, when the Monstrous Compendium Forgotten Realms Appendix 1 was released in 1989 - from here, they then made it into the Monstrous Compendium Annual Volume Three in 1996. Three years later, Dragon Magazine #257 (March 1999) featured "The Ecologies of the Firenewt & Giant Strider: Hammer & Anvil".
The firenewts' association with the Forgotten Realms likewise continued in Dungeons & Dragons 3rd Edition; they debuted in 2001's Monsters of Faerûn and were expanded upon three years later in 2004's Serpent Kingdoms.
Their final appearance to date, having skipped 5th edition, has been in Volo's Guide to Monsters for Dungeons & Dragons 5th Edition.
Both Monsters of Faerun and Serpent Kingdoms state that firenewt PCs are possible, and address the topic in some detail... but, in one of WotC's traditional cockups, neither source actually presents a functional firenewt racial writeup! Instead, you have to try and reverse engineer it from the monster writeup!