Must Have Firefox Extensions

The following Firefox extensions are incredibly useful for all kinds of web-related work:

ColorZilla - Investigate and copy colors, check coordinates, and zoom.
Googlebar - Search various Google properties, within a domain, examine the cache, and more.
Greasemonkey - Customize other people’s websites with ready-made or custom plugins.
SessionSaver - Save tab sets and histories across restarts and crashes.
Web Developer Toolbar - Provides an extensive set of powerful tools for website development and maintenance.
Xinha - Use a WISYWIG editor to easily create HTML in any standard text box.

Know of other great Firefox extensions? Please let us know.