Wikipedia, for one. I went looking to confirm what you said, and found that the canonical page for the word/abbreviation on Wikipedia was 'Okay'[1] with a redir

Wikipedia, for one. I went looking to confirm what you said, and found that the canonical page for the word/abbreviation on Wikipedia was 'Okay'[1] with a redirect to that page when you ask for 'O.K.'. The page itself says there is no consensus as to the origin of the word, and links to another page[2] with a list of possible origins. 'Oll Korrect' seems like it's the definition with widest acceptance, but it's not the only contender. I've seen 'Okay' used on other websites, though none come immediately to mind, and have never given a second thought to Facebook's spelling of the word. Even if 'oll korrect' was the origin of the word, 'okay' is still perfectly acceptable to me. It would hardly be the first English word to make such a transition.