Windowed mouse
From FTE
Name: _windowed_mouse
Default value: "1"
Flags:
0 = Disable windowed mouse support so you can use the mouse in other applications.
1 = Enabled windowed mouse support so you can use the mouse in FTE.
If the game is running in a window and _windowed_mouse is set to 1, then the mouse will control aiming in Quake. If it is set to 0, the mouse will become a Windows (or Linux I suppose) cursor, ignored by Quake.