BreadKrumbs
Build instant page to page journeys across Flickr photos. Also works as a good group promotion tool.

Steeev’s Flickr Projects
Collection of flickr greasemonkey scripts and other Flickr programming projects.

Flickr TopToolbar
Greasemonkey script or a Firefox extension, that insets a toolbar across the top of all Flickr pages

Flickr MiniToolbar
Greasemonkey script or a Firefox extension, that insets a small toolbar above the title of a photo on the photo page.

Search Plugins:Flickr
Firefox extension for searching flickr.

Flickr search plugin
A Firefox browser.

Flickrfox
An extension for Firefox (version 1.0) that lets you browse your Flickr photostreams in a sidebar.

flickReplacr
Bookmarklet to swap a flickr pic for that word.