Is Guy Fawkes Day in November not a big thing in NI? It is in England, at least. Although the traditional burning of the effigy of Catholic dissident/terrorist Guy Fawkes is becoming less common and people just are more commonly just treating it as a general holiday.
No, we don't observe it at all, in either community. Halloween is bigger here, and observed by both main communities, it's probably close enough to 5th November that we've just ended up forgetting about Guy Fawkes.
Plus it's taught in school as an English event, and we have enough of our own history going on in the early 1600s.