Another of the many changes that Facebook has made these days is, as you noted, the ‘ update of the photo viewer which now opens into a pop-up window without leaving the page where the user is located.
If you do not like this new update and want to return to the old viewing interface then we here at tricksfacebook.com have two options for you.
If you use Google Chrome or Mozilla Firefox install the script Theater Facebook Photo Killer that automatically keeps you flip through photos with the old background, without opening the new popup window.
Another solution is to update the browser to any page by pressing F5 on your keyboard (refresh). When you open the popup, just press F5 to display the photos with the old viewer, this works on all browsers.
Are you wondering what will be the point of return for the original photo viewer? Apart from the display some of the features available with the old viewer are now hidden , such as the ability to copy the url of the photo (the location of the photos on the Facebook servers) or to change the photo by clicking on "Edit".