Wow... I had no idea people set them off in such populous areas. In NYC that may be the case in the outer boroughs but somehow I don't think so, not to that extent anyway. I could be wrong! In Manhattan on the upper West Side the only real fireworks I ever saw were out on the Hudson River, the professional displays. Otherwise maybe some kids fooling with cherry bombs and sparklers off the more inland avenues along the one-way streets, that's about it. The two-way cross streets see more police patrols and there's too many stranger-witnesses along the avenues themselves, people who might call cops or go all parental on unsupervised kids playing with fireworks.
In the boondocks up here it sounds and looks like anything goes sometimes, but it's down to the usual suspects and there aren't that many anyhow. Some of them are considerate about how late into the evening they light stuff up. Some aren't. I do worry a bit about a grassfire getting started and lighting up someone's woodlot or Christmas tree acreage. If that ever happens then it's not like the deputy sheriffs don't have a clue whom to visit in future to remind about that possibility. Idiots do abound though, and they all think nothing bad will happen because they know what they're doing.
It's technically illegal in that County.... but that's probably the least of Oaklands worries
They increased significantly when most of the county's cities started to cancel their yearly fireworks during the recession. No other way to celebrate except for the trip to SF and thats just a hassle.