How to Clear Fireflies

In order to clear fireflies, you need to get all of them to stage 3 (the excited and flapping stage) at once. Each time you make an adjacent match or hit a firefly with a power tile (lily, sunflower, stripe, etc), it will progress 1 stage.

Be careful, though, because if you hit a firefly when it's at stage 3, it drops back to stage 1.