Halloween isn't as big in Europe, Matt, including in Ireland. If anything, it's a fad that's been adopted from North America. The reason they might have fireworks at Halloween might be because of the proximity of Bonfire Night... though I have no clue how much that's celebrated in Ireland either.
In England, the celebration is about the government's survival. Perhaps in Ireland, they commemorate the plot?
In Canada, I'm not sure people would set off fireworks in the middle of the street in a town or a city. You'd run the risk of bothering the neighbours, stopping traffic or even creating an dangerous accident with rogue fireworks. The point of doing it in backyards or even, and preferably, a park or a field, is that the risk of causing bother or injury are smaller. Ditto the risk of getting caught, assuming it is illegal.
Cops don't regularly patrol the streets like that here. Except perhaps on "special" occasions like a Habs game or the Formula 1 Grand Prix. And, then, they have a stronger presence downtown. Not in residential areas.
ETA We posted at the same time.
Can I just say that Mondays are haaaaard? I had a nap at lunch, and it wasn't optional. I was exhausted,