The information in the Manual of the Planes on the elemental plane of Fire is fairly minimal. Is there any more information available on the nature and character of the plane of Fire? I'm specifically interested in lore material compatible with the 3.5e-era model of the planes.
You'll be wanting the 3rd Edition Planar Handbook, whose section on the City of Brass helps flesh out the Plane of Fire as well; the 2nd Edition sourcebook The Inner Planes; and the 2nd Edition Al-Qadim sourcebook Secrets of the Lamp (if you can find it). The 2nd Edition Planescape Monstrous Compendium III offers some notes on Fire wildlife such as the waiveras and scape, but the only new indigenous creature it introduces is the fire bat (other entries such as animentals, fundamentals and ruvoka pertain more broadly to all the Elemental Planes and may or may not be of use). If you want to poke around in it, the 2nd Edition Mystara Monstrous Compendium includes the helion and pyrophor, two more unusual denizens of the plane. Finally, there is a Planescape adventure (The Eternal Boundary) that takes a spin to the plane, but overall it's nothing you wouldn't get coverage of from other sources.
You may want to ask around on Planewalker for more information or check out the work they did on their 3.5 setting conversion; it includes a section detailing the Plane of Fire.
Read The Planescape (AD&D 2e) sourcebook The Inner Planes.
The 3.5e model of the Planes is based on Planescape, which is a popular setting published about during the AD&D 2e era of Dungeons & Dragons. The book in particular that you're looking for is The Inner Planes, containing information on both the Elemental Plane of Fire and the various Planes bordering it: the Paraelemental Planes of Magma and Smoke, the Quasilemental Planes of Radiance and Ash, and all places in said planes that have more fire in them. Do note that these books date back to AD&D 2e, so the rules presentend in them do not match D&D 3.5e one on one.
Also consider tracking down the Monstrous Compendium Appendix III, which contains quite a few monsters that live on or near the Elemental Plane of Fire.