Fireworks paradox makes no sense
This movie makes no sense anyway, because as I explained once, David is in an 'impossible paradox loop'.
If David doesn't go to 1986, there's no 'missing David'. If there is no missing David, there's no 'rescuing of Max and delivering the star charts', so Max can't deliver David back to 1978 and so on. I have no coffee in my brain right now, so I can't explain it better - basically, things that happen in this movie can only happen, if other things that happen in this movie do not, and vice versa.
However, I wanted to just talk about the fireworks this time.
David's brother uses the fireworks to 'mark' the house they are supposed to travel to. He tries to do this in secret for some reason, even though that doesn't pay off in any way - everyone is outside welcoming the spaceship anyway, so what was the point in doing it in 'secret' in the first place?
However, now that David is back in 1978, they use all the fireworks, so how can there be any fireworks in 1986 for the brother to use to 'mark' the house location?
Not that that future seems to happen now, but if it doesn't, then David also can't get back to 1978, so the past can't happen, either.. David absolutely has to be 'missing for 8 years' for basically any of this movie to happen, but at the same time, if he is, then he can't be returned to 1978, because that would just erase this whole 'David is missing' stuff, so Max will never get rescued..
Maybe the only way it could make sense, if Max changed the past so much that he doesn't even admire the flowers and thus crash and lose the star charts, and also so much that he doesn't upload the star charts to David's brain.. but how can he make those decisions, if none of the 'bad things' happen, which would be the reason for him to make the decisions?
These time paradoxes are insane, no one seems to have thought about any of it while making this movie.
It's a good movie, almost a classic (although I always feel something is missing, but can't quite pinpoint what it is, besides the ridiculously stupid spaceship design - I don't mean the looks, I think it looks very cool, I mean the functionality. Allowing G-forces to affect you is not fixed by a 'chair adjustment', your ORGANS would still move all over the place and make you sick, and with enough G-forces, you would first faint, then die, regardless of your seat)...
..but dang, I wish some day writers would just STOP to think about the consequences of what they have written and how their writing contradicts itself in a major way.