Credit due where credit is due, and I'm gonna be honest. These screenshots and descriptions are from the official Bradygames guide Limited Edition. Consider buying it
There's 30 Firefly Pendants to discover and collect. Since there's bound to be spoilers in places and people, I'll put the pics and descriptions in a spoilertag. It's advised to not open this spoilertag before you've played through the story at least once.
These screenshots is nothing to write home about. If you happen to have one in better condition, I'll exchange it.