Firebombing, a violent act of bombing with incendiary devices, can be replaced with different synonyms that can suit a particular context. Some alternative words that convey similar meanings could be arson, pyromania, flaming, igniting, and torching. These words can bring in a different perspective and tone to the sentence. For instance, arson could be used to describe a deliberate and criminal act of setting a building on fire. Pyromania could be used to describe a psychological disorder that involves an irresistible impulse to set a fire regardless of consequences. However, it would depend on the context in which the word is used to make an appropriate substitution for firebombing.