The Web Developer extension adds various web developer tools to the browser.
Use the Evernote Web Clipper to save things you see on the web into your Evernote account.
YSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages.
http://yslow.org is the official open source website.
The extension previously known as GooglePreview. Inserts preview images (thumbnails) and popularity ranks of web sites into the Google, Yahoo, Bing and DuckDuckGo search results pages.
HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla. The number of errors of a HTML page is seen on the form of an icon
For Firefox 23+, you need 0.958 (under review)
A productive way to organize, read and share the content of your favorite feeds, blogs and news sites. Feedly offers a seamless transition from Google Reader.
A Statusbar with speed, percentage, time and loaded size (similar to Opera's one)
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.
The extension generates a documentmap or index of any web document structured with headings and/or with sections in HTML 5. It shows the headings structure, the errors in the structure (ie. incorrect levels), and it works as HTML5 Outliner too.
Instaright is social bookmarking platform and recommendation service.
With Instaright on a single click you can save article, links on article or text selection from article. Firefox enhancement for Instapaper. Earn badges while surfing.
Collections are groups of related add-ons that anyone can create and share.Explore Collections