Users who want that option for all Flickr photos – even those that do not offer it by default – can install the AllSizes userscript to do so. AllSizes will add the All Sizes link to every photo that is hosted at Flickr.

It furthermore extends the original functionality with these features:

• Quickly choose between any of the available sizes
• Better HTML to post photos on blogs and Flickr discussion threads
• Appends ‘(by *Username*)’ to the title and alt attributes
• Gives ‘Untitled’ for untitled photos
• Download images, copy the code to your clipboard, view the image
• BB Code for posting photos on forums and bulletin boards
• Video still images can be accessed as if they were photos
• Shortcut keys for quick actions
• Default settings can be modified
• Automatically checks for updates

As you can see in the screenshot above it will overlay the photo at Flickr with the options that it provides.Different photo sizes can be selected, downloaded, copied to the clipboard or viewed. It is also possible to display the original all sizes page of Flickr instead. AllSizes is a userscript that should work in all web browsers that support userscripts.