The person in the picture is speculating it's a bullet proof windshield, and he's mistaken (particularly from the P-39 aircraft mentioned in the link). If you look at both a P-63 and P-39 you will not find any windshield or window that is even remotely shaped like what is held in the image.
Regardless, modernly speaking, very few (if any) aircraft have bullet proof windshields. They are impractical for a number of reasons, including weight, size, thickness (distortion of picture), and efficacy. If a pilot is within small-arms distance they generally are already in trouble...
The P-63 did (example picture [0]), like many others that were designed to attack bombers and/or ground targets.
[0] https://www.flickr.com/photos/23057174@N02/3031666813