# Pastebin KjS8mXMh
let lowP = Cc["@mozilla.org/nullprincipal;1"].createInstance(Ci.nsIPrincipal);
let midP = [lowP, "http://other.com"];
let highP = Cc["@mozilla.org/systemprincipal;1"].createInstance(Ci.nsIPrincipal);
 
let low  = new Cu.Sandbox(lowP);
let mid  = new Cu.Sandbox(midP);
let high = new Cu.Sandbox(highP);

Cu.evalInSandbox("Components.classes", low)
/*
Exception: ReferenceError: Components is not defined
@Scratchpad/2:1:1
*/
Cu.evalInSandbox("Components.classes", mid)
/*
undefined
*/
Cu.evalInSandbox("Components.classes", high)
/*
[object nsXPCComponents_Classes]
*/