Facebook has recently started rolling out the cool new feature which allows you to see the photos of facebook photo album in larger size and return to the same page more quickly, I noticed the feature being rolled out to my facebook account, you can read here a complete post where I reviewed the new change in coming soon, this feature might be rolled out on your facebook profile or will be rolling out soon if you have not get this feature yet.
After logging into my facebook account, I saw this small message pop up asking to try the new feature as shown in the image below.
Once you click on the 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.
If this feature is rolled out on your facebook profile, you can download the full screen resolution image from facebook photo album, as you see the option highlighted in the image below.
This is how you can download the full size high resolution photo from any facebook photo album.