This is about how Firefox, KDE, any app you run draws to the screen. In the old world, they talked to an X server that implemented the X protocol. It's not KDE

This is about how Firefox, KDE, any app you run draws to the screen. In the old world, they talked to an X server that implemented the X protocol. It's not KDE drawing stuff to your screen, it's X, but KDE is a little special in that it can move windows around and draw title bars and borders. This is called a window manager. Two big issues with X, this was defined in the early 90s by a consortium of Unix vendors and is somewhat of an overly complicated nightmare. It's also a security nightmare, any app can snoop on any other app. Wayland is an attempt to simplify things. The server, called a compositor, is much simpler and is implemented as a library, usually by former window managers that now actually handle drawing stuff to the screen. Applications can no longer snoop, they must ask permission. If you run an older app designed for X, it uses an almost invisible compatibility shim called XWayland, basically a tiny X server that takes in X draw commands and converts them to Wayland ones. Firefox enabling Wayland support means that on most modern systems, it no longer has to use this shim. Wayland is a step forward for desktop Linux, but like any big change there are some annoyances. The asking for permission model means things like screensharing tools or apps that do weird shit like macros or capturing keystrokes need to be updated to ask permission. Nvidia didn't really support Wayland well until very recently because they got into some weird argument about driver APIs that took years to resolve.