Apple has finally depreciated Firewire with macOS 26, sadly.
Serial mice still also just work in Windows, too! If you attach a serial mouse to a USB-serial adapter, then attach the adapter, Windows should pick up and load sermouse.sys. On the flipside, if you’ve got a weird serial device attached screaming garbage out the wire, Windows might pick THAT up and load the mouse driver, too… “hey, why is my cursor freaking out?”
Serial mice still also just work in Windows, too! If you attach a serial mouse to a USB-serial adapter, then attach the adapter, Windows should pick up and load sermouse.sys. On the flipside, if you’ve got a weird serial device attached screaming garbage out the wire, Windows might pick THAT up and load the mouse driver, too… “hey, why is my cursor freaking out?”