You can respond to the trigger by cracking a fetch. Once the trigger resolves, you can't crack a fetch. Just be sure to be clear to your opponent what is happening, and don't get caught in a situation where you pass priority without fetching, or a pedantic opponent will call you on it (once you pass priority and they pass priority, you can't fetch anymore).

As for Firespout, howabout Bonfire of the Damned instead? More mana intensive, but it's one-sided, hits all creatures (sans protection) and is actually castable without miracle, and splashable with its solitary R requirement.