I have a purple firefish they are lovely fish, very attractive, he is out most of the time, not aggressive, although he does headbutt my yellow assessor occassionally but nothing worse. He darts into his cave when spooked, then at lights out he heads straight for his cave and stays there till morning.
They can also jump when startled so a covered tank is best for them
If I remember correctly its advisable to keep only one though, as they are aggressive to each other
I believe (and I could be very wrong so please double check) that Helfrich's Firefish and the zebra firefish can be kept in groups as they are less aggressive to their own kind then the rest. Like I said though this is just a vague bit of info i THINK i remember so please dont take my word for it
They are the only ones I know of. I have kept the red and purple ones, they can hide up a lot if there are more aggressive fish around but they are nice fish and I second all that Trod has already said. A tight fitting lid is a must have as they spook easierly and will jump.