I think it would depend on how many fireflys you would want. You could use Hypervoxels in sprite mode.
Here's a VERY simple logo I made with this technique.
http://bigdogvideos.com/movies/logo2a.mov
If it's just a few fireflys, I'd do points, animate them, and make the texture the image you want, along with some luminosity to create the "firefly" effect.
Hope that helps.
Hoop