I see this firefly effect in various places while in the CS, but I have never seen one in the game. I have seen plenty of butterflies. Does the firefly effect work, or am I missing something (probably stupid)?

Thanks.

If you right click on it in the CS one of the menu options is "Use Info" which will show you where it's been placed. Then you can go there in game and see it.

I have seen it in-game, but it may be one of those things that depends on your game settings. So open up the options menu when you get to a firefly location and tweak a few things.