I have a hard time believing this isn’t a shitpost project.

It is currently a hidden setting in Firefox’s about:config. They are removing it from there and no longer controlling it within Firefox itself so it will follow the setting set in you window manager (probably have the wrong term here, haven’t had my coffee yet), which is (generally) not hidden and available through a settings GUI. So you won’t have a web browser having different functionality than elsewhere on your machine.

If it’s hidden at that point, blame the window manager/desktop environment/whatever it’s called.

They are setting this as an optional feature. They are not just disabling it.