Facebook recently introduced a new way of browsing photos and albums. The new photo viewer uses the lightbox technique whereby the page is dimmed and a box is overlaid with a larger version of the selected image.
Some of the improvements it brings are the ability to stay on the page without having to go back in your browser’s history (you simply hit the close ‘x’ button and you’re back to where you were), faster photo flipping/browsing and the ability to download a high res version of the image (if available).
For those who hate this lightbox preview, you may switch to the old fashioned way by simply opening the picture in a new tab (hold ctrl key + click) or a new window (hold shift key + click) instead of simply clicking on the picture. You may then continue browsing in the new tab/window the same way you were used to.