An automatically generated list of my installed add-ons
NOTE: Xmarks lives! Learn more at http://blog.xmarks.com . Xmarks is the #1 bookmarking add-on. Keep your bookmarks, passwords and open tabs backed up and synchronized across computers and browsers.
Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...
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.
Show the IP address(es) of the current page in the status bar. It also allows querying custom information services by IP (right click) and hostname (left click), like whois, netcraft, etc. Additionally you can copy the IP address to the clipboard.
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)
Secure Login is an extension for Firefox integrated password manager.