It's not actual first person view but I created an artificial one looking out of a part. I have tried changing the value of MouseDeltaSensitivity and I noticed that it only works if you are holding down the right mouse button (moving the camera) and not when I'm in my first person.
Second, I looked into camera manipulation like getting the panspeed and tiltspeed but the api says that these are broken and should not be used.
How do I go about slowing down how fast the mouse can cross the screen or offset how fast the camera follows the mouse?