When you view a picture on Facebook, it's displayed in a "light box," meaning that it seems to rise off the page -- together with all accompanying data like owner, album name, description and tags -- along with two black bars to either side. In this view, a Facebook picture is shrunk to the dimensions of your browser so that you do not have to scroll to see the whole picture at once. To make the pictures bigger, turn off the light box.
Log in to your Facebook account at the Facebook website.
Click "More" in the left-hand menu column if you do not see a "Photos" link, then click the "Photos" link. This displays your friends' most recent photo albums.
Click a photo album to view the first picture in that album. The picture displays in a light box and is therefore sized to fit within the frame of your browser without scrolling. You can arrow right or left to scroll through the pictures in that album inside the light box.
Place your cursor in the address bar of your browser at the far right end of the displayed URL.
Delete "&theater" -- it appears without the quote marks -- from the end of the URL and press "Enter." The page reloads without the light box and the picture is now displayed at full size. Arrow right or left to scroll through the pictures in that album at full size.