nsICollection
inherits from: nsiserializable last changed in gecko 1.7 method overview void appendelement(in nsisupports item); void clear(); pruint32 count(); nsienumerator enumerate(); nsisupports getelementat(in pruint32 index); void queryelementat(in pruint32 index, in nsiidref uuid, [iid_is(uuid),retval] out nsqiresult result); void removeelement(in nsisupports item); void setelementat(in pruint32 index, in nsisupports item); methods appendelement() appends a new item to the collection.

nsIPrincipal
inherits from: nsiserializable last changed in gecko 2.0 (firefox 4 / thunderbird 3.3 / seamonkey 2.1) for details on principals, how they work, and how to get the appropriate one, see security check basics.