It used to work like a charm, but a few days ago the emote button suddenly disappeared every time I clicked on it. I can still see others using them in chat but I can no longer use them. No idea what caused it since I didn't change anything, it just happened over night and reinstalling just stopped the emote button from appearing at all.
Update: Can confirm what Shiro wrote, disabling the add-on "Ghostery" on Twitch lets the emote button work again as intended. However there was no conflict before, would be nice if they can work together again.