Keep in mind too Feanor's attitude toward Morgoth, and his [Feanor's] way of working:
'... for none of the Eldalie ever hated Melkor more than Feanor son of Finwe, who first named him Morgoth; and snared though he was in the webs of Melkor's malice against the Valar he held no converse with him and took no counsel from him. For Feanor was driven by the fire of his own heart only, working ever swiftly and alone; and...'
And after Feanor crafted the Silmarils, Morgoth: 'From that time forth, inflamed by this desire, he sought ever more eagerly how he should destroy Feanor and end the Friendship of the Valar and the Elves.'
Brego in his first post writes: 'Who knows, as Morgoth hated Feanor more than any other Elf, perhaps he found a way of afflicting him with some unknown new thing. He and Sauron managed to create plague like diseases which effected Men in later ages.'
But Melkor sowed lies rather than some unknown new thing or disease, if subtly; and conjured visions (in the hearts of the Elves) of mighty realms that they could have ruled at their own will; and by this poisoning (among other lies) he reached Feanor indirectly, for Feanor burned with a desire for wider realms and 'freedom' from the Valar.
Generally speaking this wasn't only something Feanor felt, for even though Galadriel swore no oath, she too (at least) 'yearned to see the wide unguarded lands and to rule there a realm of her own', kindled by the words of Feanor himself.
Of like mind with Galadriel was Fingon, also being moved by Feanor, as well as others of the Noldor, kindled with the desire of new things and strange countries.