Elbereth wrote: Ok, then we might think that maybe Feanor has no disease but he was the first Elf that felt hatred.
I won't quibble with the word hatred here, but I'll add that Tolkien does note bitterness among his Elves even before Feanor was born for example [for instance, however taken out of context here for sake of brevity: 'This ill-feeling descended in part from the bitterness of the Debate before the March of the Eldar began, and was no doubt later increased by the machinations of Morgoth' JRRT, Quendi And Eldar, The War of the Jewels]
And Melkor had cozened many of the Noldor before Feanor had reason to 'hate' Morgoth specifically: the Silmarillion notes that many of the Noldor leaned towards Melkor, and (noted later) that the Noldor even began to murmur against the Valar, many becoming filled with pride.
Yes Feanor was among them at this time, but the Silmarillion relates that Morgoth had kindled the hearts of the Noldor to strife, and of their quarrels came at length the end of the High Days of Valinor. Feanor was the first to speak 'openly' against the Valar, and so at first the Valar guessed that he was behind the discontent.
But ultimately Melkor came to Feanor at Formenos, and Feanor pondered 'if indeed he might yet trust him so far as to aid him in his flight' -- but Morgoth overreached himself and awoke a fire more fierce than he designed, and Feanor then pierced 'the cloaks of his mind' [Melkor's mind] and found there Morgoth's lust for the Silmarils. 'Then hate overcame Feanor's fear...'
And the subsequent slaying of Finwe and theft of the Silmarils... well that didn't help
In any case, one need not imagine Melkor, while captive, doing something to Miriel and Finwe, nor that Morgoth cursed them in Middle-earth before his captivity.
Judging from an earlier post, Brego appears to think so (although I assume it's one or the other at this point, not both] because he finds something problematic with Tolkien's God Eru 'allowing' something, and so Melkor is injected in a way that Tolkien did not employ him.
In my opinion the story needs none of this however. To my mind all one need do is embrace Tolkien's notion of God, Free Will, and Arda Marred, and there is no reason for Morgoth to be cursing Finwe and Miriel before her desire to die. And the author can be quite clear when he wants the reader to imagine a specific curse upon a given person or family -- thinking Hurin, for example.
For the debate of the Valar regarding the case of Finwe and Miriel, see Laws And Customs of the Eldar, Morgoth's Ring. And for an interesting statement from Miriel...
'My life has gone out into Feanor, my son. That gift I have given to him whom I loved. I can give no more. Beyond Arda this may be healed, but not within it.'
JRRT, Finwe And Miriel, version 4, Of The Silmarils And The Darkening Of Valinor, [subtitle Of Finwe And Miriel], Morgoth's Ring