The Web Developer extension adds various web developer tools to the browser.
View HTTP headers of a page and while browsing.
Firecookie is an extension for Firebug that makes possible to view and manage cookies in your browser
Firecookie is part of Firebug since Firebug 1.10
An extension that allows for the use of dynamic commands in Firefox.
A maintained version can be installed via: https://bitbucket.org/satyr/ubiquity/downloads/tip.xpi