Anyone familiar with Flickr would know that the size of any uploaded image differs from the original image,in the photo view page . And if you want to view full size in a single click , you can use this Firefox addon .

Flickr original Firefox addon analyzes the original structure of Flickr URL and extract the image ID .This image ID is used by a web service that uses the Flickr API to out put the Flickr photos in full size .Hats off to jzlabs for this wonderful addon .This addon is still in the experimental stage .So at the Mozilla site ,you would need to sign in .  Instead of that , you can download the Flickr original addon here .