Nebraska honors permits from states whose requirements to obtain a permit match or exceed Nebraska's. As far as I have found, Mississippi doesn't require training for a permit. Just file an application and pass a background check. The state also has an "enhanced" permit which does require training. Holders of the enhanced permit are authorized to carry in many, but not all, places forbidden to holders of the ordinary permit. You might write to Nebraska's attorney general to bring Mississippi's enhanced permit to his attention and request that he reconsider honoring it.