Firemaking is by far not the only Skill, that only costs money (though it is the only one, that literally burns it). Neither is Firemaking completely useless (at least Jagex tried a lot not to let it look useless): It is required to complete a lot of fun or rewarding Quests (Tears of Guthix, First Resort, Desert Treasure, Enakhras Lament, Lunar Diplomacy, Legacy of Seergaze, Sea Slug, Swan Song... It lets you wear a lit Mining Helmet, that looks great and never gets extinguished in a dark area, So you could never ice-barrage, blood-runecraft, balloon-travel, monkfish-fish, or collect blue Tears with your Platypus without this Skill. Maybe this is, what Firemaking will be for a very long Time (or for ever): A Quest-Skill