You will need to install a user script manager extension to install this script.
Adds links to any Flickr individual photo page, pointing to the available sizes of the photo. While the links are fetched in the background, an animated 'loading' message will show. Image sizes are sorted according to type: Square, Small, Medium, or Large.
For the newest 2014 version, the links appear below the view count and rights info. In the 2013 layout, they appear in the sidebar below the description.
GreaseMonkey menu commands allow you to toggle which image links you get (turn Square off, for instance). You can also set it so the browser automatically downloads the image you click (by default, clicking a link merely loads the image in your browser, or you can right-click it to save it).
The script uses jQuery 2.0.0, as hosted on GoogleAPIs.