The Dinobots had fire-breath included in their alternate modes. Although they all possessed the ability, Grimlock and Slag were the only ones that really employed it. Wheeljack had Grimlock demonstrate his mastery of his fire-breath by adjusting Blaster's volume levels. Later, while practicing on Dinobot Island, Grimlock had Slag practice his "fire stuff" (Grimlock's words) by evaporating a pond. Slag displayed good moves. The local wildlife was not amused. Later, Slag's fire-breath saved the Dinobots by evaporating the tar pit they had sunken into, but it made him rather tired.
During the brawl among the Primitives, Grimlock showed the upity Decepticons not to insult him by unleashing his fire-breath upon them. The Decepticons hit started to cough...cause that's what happens when you get him with fire that can melt body armor. It may be possible that Grimlock deliberately turned down the power of his breath, wishing only to subdue the Decepticons (since at the time he was allied with them), but a) this is only speculation, and b) Grimlock isn't that smart (or at least wasn't in the G1 cartoon).
Scourge had the ability to activate two extra, fire-breathing reptilian heads as his cyber key power. This attack was used in several scenes as a suppressive attack, but was also blocked or simply ignored on occasion by powerful characters.
Megatron had fire-breath installed in the Dinobots, intending to unleash it against the humans and Autobots. When Isaac Sumdac confronted him about its presence, Megatron claimed that his desire to have a body once more compelled him to experiment by installing the fire-breath as one of several "features". Sumdac bought it hook, line, and sinker.