View HTTP headers of a page and while browsing.
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
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.
TinEye is a reverse image search engine. The plugin adds a context menu item that allows you to search for an image to find out where it came from, how it is being used, if modified versions of the image exist, or to find higher resolution versions.
AddThis for Firefox is the best add-on to make sharing and bookmarking simple. Have all your favorite web 2.0 social networking, bookmarking, blogging, and e-mail services at your fingertips. Share any page, anytime, with anyone.
Integrates location bar and search bar into one. Shows search and url suggestions. Quickly switch search engine using search keywords. Provides different auto-complete popup styles for compact displays.
Adds toolbar buttons to the customize toolbar window in several programs including Firefox, Thunderbird and SeaMonkey. Some of the buttons make commonly preformed actions quicker, others add new functionality.
Collections are groups of related add-ons that anyone can create and share.Explore Collections