Btw, flash powder (at least the pyrotechnic variety as opposed to that used for camera flashes) is actually a primary high explosive.

Primary = easy to activate, doesn't need an explosive initiator. High explosive = detonates rather than deflagrates.

And for bonus points, most flash powder is self-confining in very small quantities. Means a little pile of powder will detonate even if not enclosed.

You could sure make decent explosives with OTC fireworks though - in the early 90s we would buy hundreds of those whistling fireworks, hammer them, cut the bottoms off, and then fill various bottles with all the powder. We made a shockwave with one of our makeshift bombs and decided we should probably stop after that.

In most states you can go buy all the tannerite you want. That's an actual explosion

https://www.youtube.com/watch?v=5VaLtf_EIVQ

The old school whistling fireworks were often based on picrate chemistry. Picrates famously have the ability when burned to hover between normally deflagration and true detonation; the whistling is a side effect of this. One of the largest non-nuclear explosions in history (see below) was a picrate explosion. These aren’t used anymore for safety reasons; they don’t have a great stability profile and picrates are true high-explosives.

Over the years they have found alternatives for and phased out most high-explosives used in fireworks. Many high-explosives will just deflagrate/burn but can spontaneously detonate with considerable power if the conditions are right, which makes them dangerous.

https://en.wikipedia.org/wiki/Halifax_Explosion

Have advances in explosives, fuses and quality control made fireworks safer in the last 40 years?

Or perhaps the safety improvements are offset by sellers now offering bigger fireworks (either because those are now actually safe and both buyers and sellers are more comfortable with them, or just because of a general hedonic improvement).

Or perhaps they are safer for their users, but worse for starting fires or interfering with low-flying aircraft.

Either way I would be interested in reading more about this, something more nuanced than "fireworks dangerous". At the least it's a counterpoint to what happened with illegal drugs which seem to have become more dangerous as a result of regulation and bans.

I think the improvements in consumer fireworks safety has been incremental. The fuses are more reliable, they’ve reduced the use of mercury and other heavy metals in pyrotechnics, and they’ve moved toward more stable chemistries. That said, I think regulation is marginal at best so who knows what a random firework will actually do. There are also practical constraints on the kinds of chemistries that make good fireworks e.g. you don’t want potential high-explosives to be something you can buy over-the-counter by the kilo.

There is a parallel in military explosives research. For example, the US military is slowly moving toward “insensitive munitions” which use explosive chemistries that are nearly impossible to detonate accidentally due to fire or impact. This originated in nuclear weapons research but has spread to other weapon systems.

Fireworks are intrinsically dangerous in the hands of incompetence, ignorance, or stupidity. No amount of engineering can solve that problem unfortunately.