I see in some cities fireworks are used often also to open a new store, wedding....and so on

In the small little village I call home, fireworks are a daily event. For a weekend day, they start around 8-9 a.m. and will be spread out throughout the village, maybe 10 different times during the day. Those are just the large pack's that just shoot up to make a loud noise. As far as the pretty ones that are fun to watch, that only occurs maybe once a week around here.

But this all depends on the city's laws... most bigger cities have strict laws against all the free use of fireworks in the streets.

1st tiers cities or more densely populated cities might have laws against them but enforcement will vary

If everyone else is doing them then go for it. I'm in Guangzhou and I've seen huge, untended fires just burning in the streets during festivals so I don't think they'd freak out too badly over some foreigner doing fireworks.

I was in Xi'an during Spring Festival once, and there was a guy selling big boxes of fireworks from a table in the street. On the table were all the boxes of fireworks spread out - some opened up to show what was inside. He was holding a baby in one hand - his son I think - and in the other hand he was using a lit cigarette to light a firework next to the open box on the table - NEXT TO THE BABY'S HEAD!!

It's a wonder nobody caught a whizz-bang in the face.

Fireworks? Allowed? No laws here and why wait for a festival? Fireworks almost every day to celebrate something be it personal reason or whatever. Sky rockets in flight, afternoon delight....goes the song. Outside your window, in the courtyard, on the street.
During festival time the main road is full, I mean full, of people selling fireworks from the roadside. Boxes and tins stacked up, maybe 500kgs in each stall and there are literally hundreds of stalls. One errant cigarette and you would have the greatest fireworks display in history.
So go and buy, light, enjoy, any day you like.