[falcolas]

Facebook is not a Nebraska company, and the user being in a separate state would make this an interstate commerce issue. Facebook would be justified (I'd personally say it's their duty to) in refusing, and letting it bubble up into the courts and let the federal government decide.

[googlryas]

That's pretty much how it works - you file a subpoena from a foreign jurisdiction, and then the state court helps forward it, for example see Delaware § 4311