They are slightly toxic, sometimes even to humans
SO, wash your hands after handling. Of course, if you don't lick your fingers after touching them your probably pretty safe. Just cause a frog is toxic, it doesn't mean it will kill you! Some people do get nasty reactions, especially when they accidentally rub their face or eyes after handling the toads though, so you still should be careful about handling them.
I have heard that some people get allergic reactions to the toxins, in the form of a light rash...but this is very very rare.
They can however potentially damage other species! I got a letter from a visitor who told me that she put a Pac Man Frog twice the size of the firebellied toad in the same tank. Less than 5 minutes later the Pac Man Frog was dead...the toxins in the firebellied toad's skin had killed it!