Facebook has massively rolled out the new Photo Viewer to many users, which is an exact copy of the Google+ photo viewer.
The new Facebook Photo Viewer has comments on the right side of image, while dimming the background content of that page.
But you can by-pass that photo viewer very easily, to view photos in old style.
For that, simply open that image in a new tab on your browser, either by clicking the image with you middle mouse button, or hold the ctrl key & click on the image.
This will open the image in a new tab of your web browser, but in the same old facebook style!!