This is a cool trick you can do and event though it doesn't last long it is still cool to see.
Step 1: What Is Needed
To do this you will need the apps Minecraft (with a creative world), Textures for Minecraft PE, and Block Launcher (to launch the texture pack). Go onto Textures for Minecraft PE and go to 0.10x Textures and download the texture pack called Super Mario Craft. Then on to Block Launcher and go on your creative world.
Step 2: Preparing
Find a flat place to make the fire flies. You will need TNT and Flint and steel now place the TNT.
Step 3: Seting the TNT
Now Place fire all around the TNT but don't actually set off the TNT. Now stand back and wait for the explosion.
Step 4: The Tecnical Stuff
When the TNT explodes you should see the remaining sparks from the fire witch are the fireflies. You can do this without the texture pack but it wouldn't look the same.