What exactly does this function do? (Thunderbird, Mac)
P.S: I wrote you a few private messages. Do not if you have already seen them.
Which "this function"? Do you mean the preference extensions.pEp.importRNP? That is used from import of keys from Thunderbird's OpenPGP solution which uses a library called RNP. RNP import may be shipped in a future version, for now, its development has a low priority.