Today, when I logged into my facebook account, I noticed a new feature has been rolled out across my profile which allows to see a facebook photo in full size, which is appearing on your facebook wall. This include all the photos which appears on facebook wall, so you can preview and comment on the photo in full size and return to the page quickly as the pop up messages said shown in the image below.
Just when you click a photo, it will appear in large size supported as per your monitor screen resolution and it will appear as a black colored pop up window with in the browser with photo in the center and comments at the bottom center of the window as shown in the image below.
In order to close this pop up window either press esc on your keyboard, click close button on the top right corner of this window or click anywhere outside the window in your browser.
Additional Tip: You can scroll through other images in the same photo album quickly through left or right arrow keys on the keyboard