When somebody adds multiple photos in a Facebook post, the gallery is shown in a nice pretty mosaic view on your timeline. If there are more photos in the album than are shown, theres a small "+number" on the bottom right image.
One might think clicking the "+n" would expand to show more photos in the mosaic. Instead, clicking the "+n" only opens the last photo (red) in the pop up window.
Here's a mockup of what I wish clicking the "+n" button would do: expand the album mosaic to show the additional photos.
Somewhat related to this: I'd love to see Facebook add a filmstrip to the bottom of the photo viewer pop-up window. It makes it easier to navigate through albums by giving you a bird's eye view of the context of the album.