How can I unstick lollies stuck in a jar, welded by heat?

You could try freezing them, if you want to remove them from the jar cleanly. However, it's possible all humbugs will stick together.

You could also try heating it (microwave shortly, or put it in the sun again), and remove bits while they are still warm. I would put the jar afterwards in the dishwasher to remove residuals.

However, I'm afraid both methods won't be able to have the individual humbugs out.

Try sprinkling cornstarch over them. Lollipops usually get stuck because of humidity, and the cornstarch would absorbe that humidity.

It depends on how tightly they are stuck together. They may or may not be salvageable.

If they are not stuck together too badly, you may be able to pry them apart with a butter knife.

The next thing I would try is putting warm water into the jar and letting them soften up, then trying to pry them apart, again with a butter knife. They will be unreasonably sticky, so you will want to dry them on something they won't stick to like a silicone mat or parchment. I would then try to dry them in a warm oven (its lowest setting) although they will probably always remain sticky as sugar is extremely hydrophobic.

If that doesn't work, you can use boiling water to slowly dissolve them until you can get enough out to at least recover your jar. It may take a couple of changes of the water.

so i was trying to do some weird experiment and melt jolly-ranchers. However they stuck to the bowl. I COULD NOT get them off. So what I did was put a little water in the bowl. Then I microwaved it for 30 seconds checking on it every ten. After the thirty seconds I took it out, (Be careful it's hot) and changed the water. I did this till the ranchers were eventually gone. I don't know how it would work for other candy but it worked great for jolly-ranchers.