Different wavelengths of light scatter more or less as they pass through gas or dust. This is why the Earth's sky is blue on a clear day, and sunsets are red --- the red light scatters less, blue scatters more.

In smokey or smoggy air, the red light is also scattered.

The "smoke" in a nebula is mostly gas and dust. It's either left-over primordeal matter (hydrogen gas, some helium), or ejecta from novas and supernovas --- star-smoke if you will, though it's created by nuclear fusion rather than chemical combustion.

JWST's IR sensors can cut through that dust more readily than Hubble's optical-range sensors could, and pull out more detail on the dust to boot (based on my own viewing of comparative images).

I'm not sure if the dust is reflecting light or glowing from heat, though my hunch is it's mostly reflecting. Stellar gas that gets hot enough will also glow in infrared (or higher) wavelengths, and that might also be picked up by JWST. I suspect there will be targets demonstrating this in future.