When viewing 'All Sizes' of a Flickr photo, this sets all photos to be viewed with the page's body width.
When viewing Flickr's 'View all size" page, the larger scale photos can be a little annoying if you're not looking to pixel-peep. This extension simply sets a standard width for those photos so they don't extend off-screen. Likewise, the very small photos will be stretched to fill their allotted area, meaning their compression will become very obvious. This is meant for the average person that just wants to open the window and get an instantaneous view of the photograph.