Facebook has introduced a new photo viewer on their network which popups instead of loading a new page.
There is no way to disable this new functionality. But for now, you can get around it and browse photos in the old fashioned manner.
There are two tricks you can use. You can double click on photos to manually open them in a new Tab/Window.
Or you can press F5 when the photo viewer popups open up on clicking. That should take you to the photo page as well.