Download Original Flickr Image
When a user uploads a photo on Flickr, it resizes it to various sizes and gives viewer the choice to view in whatever resolution (size) he wants.
Similarly, if you want to view or save the original Flickr image, you have to go all the way through the photo page and select Original from the sizes available.
Flickr Original is a Firefox extension that lets you directly download or view the original Flickr image. You just have to right click on the image, and it will show you the option to download or view it.
This extension will not work with images with disabled downloads. Flickr Original is currently an experimental Firefox add-on, so download it from the developer’s page.