Firefly is a term popularly used for certain tropical American click-beetles (Pyrophorus), due to their power of emitting light.
The name "firefly" is often applied also to luminous beetles of the family Lampyridae, to which the well-known glow-worm belongs.
1-liguchi of Hirado is to be classed with ceramrsts of the new school on account of one ware only, namely, porcelain having translucid M d decoration, the so-called grains of rice of American ~ collectors, designated holaru-de (firefly style) in Japan.
The cucujo or Cuban firefly (Pyrophorus noctilucus) gives out so strong a light that a few of them serve effectively as a lantern.
If you've not seen a single episode of Firefly, honestly - you're missing out, but not to worry because Whedon has written Serenity to give enough of the show's background for non-fans to be able to follow his story.