Fire shrimp come from deeper waters than other ornamental shrimp available in the trade. Their red color at depths makes them look black. They are cryptic snimals, and in my personal experience seem to be more social and viewable if kept in pairs. Shrimp have the magical ability to change sex based on need called sequential hermaphrodites, therefore, if you get two shrimp you will eventually have a male and female pair.
The only issue that i have ever seen with the fire shrimp is in bagging/shipping them together. They tend to cannibalize one another in shipping/bagging, so they do best when bagged individually. As long as you get them bagged separately, they will generally inhaibit a tank peacefully, with other species of shrimp. At any given time at the shop we have from 2-6 fire shrimp hanging out in the same 33gallon aquarium with no issues!
These guys generally do well with other shrimp with the exception of the coral banded. I have seen large agressive coral banded shrimp kill new shrimp additions out of sheer joy, not even attempting to eat the body of the deceased individual. IMO coral banded shrimp should be kept alone, but Fire, peppermint, and cleaner, can all be kept together peacefully in an adequately sized aquarium!
hope this was of some help!
cheers~!
jon