Drivers are software that runs in the kernel to interface with hardware.

Firmware is software that runs on the actual hardware itself, in this case it runs on the microprocessor on the WiFi card

firmware support involves supplying the binary blobs that the driver needs to upload to certain peripherals like intel wireless cards.

personally i would like to see non-free software kept out of the main disc images but the images including firmware being more visibly advertised and it made clear on the download pages what hardware requires it and who needs it.

So the firmware for a certain WiFi card is the same, no matter if you use Linux or Windows of MacOS? And it is provided by the manufacturer of the Hardware?

And some WiFi cards works out of the box with Debian? Is that because the manufacturers of those cards provided the source of their firmware or because open source alternatives have been written by somebody else?

There are a few models that don't need a firmware blob or where the manufacturer provided source code for it (mostly pre ac Atheros chips).

firmware is specific to chipset and are binary blobs supplied by the manufacturer. ath9k-supported and generally realtek cards don't need firmware; theo de raadt noticed the culture difference between american vendors like intel and broadcom who leave the functionality to the firmware so they can be first to market, and chinese vendors like realtek who take their time to best fit customer needs