Haha, sorry about that. Your guppy fry I mean. If you have other fish in the tank, it is highly recommended that you don't add salt. It WILL stress them out.
Here is the delio, mollies do not need salt to survive. They will do perfectly fine in fresh water. However, they originally were brackish fish in the wild. They are now today able to survive in freshwater because they were introduced to the hobby so early in freshwater and have been "weaned" (I don't know how else to put this) onto it where now their ancestors ancestors ancestors were brackish, but the decendents have all been in freshwater and they have now adapted to it (the ones sold at pet stores, not the ones in the wild). So the myth is not that they aren't brackish, but that they need salt in the water. I hope that explains better.