I don’t think a person who’s been dead for over forty years minds much. It was to celebrate his memory.
In France like apparently in many other countries, it celebrated on June 24 (St John).
I say celebrated, but actual celebrations have become rare. In the small village in southern France where I was raised up, it’s still done, but I couldn’t tell whether it’s common or rare in the countryside in general.
Everybody gathers and a whole tree is burnt at night, and people jump above/through the fire when it’s possible. I can’t even remember what such jump is supposed to bestow. Luck? Marriage? Mostly done for the fun, anyway. There’s often some wine to drink.
I remember that when I was a kid, my grandmother would take a small bit of coal from the fire and would draw a cross with it on the doorstep of the house. I don’t know and I think never thought to ask why she did so exactly.
Also, it seems that in some towns there’s a firework during the weekend closest to june 21. Not particularly common, though.
So, contrarily to northern countries, celebrations aren’t nearly as important here, when they even take place. I’d bet a large part of the population isn’t even aware they exist.
The fires in Finland are usually tall enough that even the people most drunk don’t try the jump. I’ve never even heard about jumping as a custom in Finland.
The fire sounds like a pagan more than Christian tradition, particularly at a specific astronomical date. This is a really stupid date to have a bonfire anyway because the night is not dark at all.