Do you have a link for that? When I read the statute, and its history, I saw that Montana had initially stated it would defend a Montana citizen in federal court, if the feds attempted to enforce federal law over the Montana law. That provision (just to use the Montana AG to defend its own law) was removed before the Montana law was enacted.
Wyoming gov. signs bill on federal gun regulation – 3/11/10 The WFFA differs from the original Montana model in that it establishes potential state penalties for anyone arresting a Wyoming person making or selling firearms, ammunition or accessories done in compliance with the WFFA.
From the text of the bill:
6-8-405(b) Any official, agent or employee of the United States government who enforces or attempts to enforce any act, order, law, statute, rule or regulation of the United States government upon a personal firearm, a firearm accessory or ammunition that is manufactured commercially or privately in Wyoming and that remains exclusively within the borders of Wyoming shall be guilty of a misdemeanor and, upon conviction, shall be subject to imprisonment for not more than one (1) year, a fine of not more than two thousand dollars ($2,000.00), or both.
As far as state helping with federal defense:
6-8-405(c) The attorney general may defend a citizen of Wyoming who is prosecuted by the United States government for violation of a federal law relating to the manufacture, sale, transfer or possession of a firearm, a firearm accessory or ammunition manufactured and retained exclusively within the borders of Wyoming.
Which sounds redundant insofar as it may conflict with (b). If you arrested the fed while he was trying to infringe on your citizen's rights, how did that guy's case ever make it to court? Belt AND suspenders I guess.