Firestone

The Firestone is the most basic dragonstone used by Manakete class characters and, mostly, enemies. It grants numerous staticical bonuses to enable the normally feeble Manaketes to fight quite effectively.

Akaneia Saga
In Fire Emblem: Shadow Dragon, (and, of course, FE1 and FE3.) two can be obtained and used by both Bantu and Tiki.

Fire Emblem: Fuuin no Tsurugi
In Fire Emblem: Fuuin no Tsurugi, it cannot be obtained normally, however, one can obtain it through use of glitch,(see below.) so that Manakete Fae can fight even after her Divinestone has broken.

Firestone Glitch(FE6(Continued from above.))
This is a glitch performed in Chapter 23 in order to obtain a Firestone for Fae:
 * Step 1: Bring a thief, (Preferably Chad, although Astol and Cath do just fine as well.) and make sure their Speed stat is higher than that of the Manaketes in the chapter.
 * Step 2: Move your Thief of choice with 6 spaces of the Manakete you wish to steal from, and make sure they are within the range of the Druid weilding the Berserk Staff. Also make sure that the Manakete is the only enemy (or ally, for that matter) within range of your Thief. It is recommended that you hit the Manakete with a Sleep Staff first.
 * Step 3: Let your Thief get berserked.
 * Step 4: Next turn, your Thief should steal the Firestone from the Manakete. Use Restore to cure the berserk status, and give the Firestone to Fae.

Fire Emblem: Sacred Stones
In Fire Emblem: Sacred Stones, the Great Dragon Myrrh comes with a Dragonstone, which is very similar to the Firestone item.