The Web Developer extension adds various web developer tools to the browser.
Seoquake is a Firefox SEO extension aimed primarily at helping web masters who deal with search engine optimization (SEO), social media optimization (SMO) and internet promotion. Seoquake allows to investigate many important SEO parameters.
Screengrab! saves webpages as images... but not for new versions of Firefox.
FF changes too fast and I don't have the time to maintain it anymore. Bugs have developed that I am not in a position to investigate.
Therefore, Screengrab is EOL.
ScribeFire Classic is a blog editor that integrates with Firefox and lets you easily post to your blog.
ScribeFire Classic is no longer supported; you should install ScribeFire Next: https://addons.mozilla.org/en-US/firefox/addon/scribefire-next
Cool utility for cleaning up a page (for printing or better viewing) as well as for web development. Displays a red rectangle on the element under the mouse -- hit "w" to go wider (get the containing element), then hit other keystrokes to remove, etc