Here is a list of links to the Firefox extensions that I use on a regular basis.  Firefox is a free, opensource, cross-platform browser that is notible for it's speed and security.  It offers innovative features such as tabbed browsing and has an astounding lack of ActiveX ;)

Firefox is based on the source from the Mozilla Application Suite, which is based on Netscape Communicator.  It is my browser of choice because of the functionality and security.

NoScript 1.1.4  - NoScipt allows the user control over the scripting embeded in web pages
CustomizeGoogle 0.46 - enchanced customization of everyones best friend
IE View 1.2.7 - adds 'open page in IE' option to right click menu
PDF Download 0.6 - adds user options for opening PDF files in FireFox
DownThemAll! 0.9.8.7 - allows user to download all links on a page, very customizable
Adblock Plus 0.7 - greatest thing since sliced bread.  Blocks ads on the internet
Adblock Filterset.G Updater 0.3.0.3 - works with Adblock and automatically updates your ad block filters
Download Statusbar 0.9.4 - moves the download manager to the status bar
Sage 1.3.6 - RSS feed reader for FireFox
Add Bookmark Here 0.5.5 - adds link in Bookmarks to add current page 'here'
Slashdotter 1.5 - essential for slashdot addicts
BlogThis 0.3 - haven't used this much yet, hope it works well
Gcache 0.2.4 - adds 'open gcache of this page' option in right click menu
del.icio.us 1.0.2 - social bookmarking site
Gmail S/Mime 0.1.9 - experimental, adds ability to use signed,encrypted mail for gmail.