Here are the Firefox Extensions I've found to be most useful:

  • ColorZilla -- Advanced Eyedropper, ColorPicker, Page Zoomer and other colorful goodies (http://www.iosart.com/firefox/colorzilla/)
  • Session Saver -- magically restore your last browser sessions pages (http://adblock.ethereal.net/alchemy.cgi/SessionSaver)
  • IE Tab -- Open IE only pages in embedded IE (http://adblock.ethereal.net/alchemy.cgi/SessionSaver)
  • Livelines -- Add RSS feeds to Bloglines or Sage with the RSS icon on the location bar (http://heygom.com/extensions/categories/livelines/)
  • Greasemonkey -- Greasemonkey is a Firefox extension which lets you to add bits of DHTML ("user scripts") to any web page to change its behavior. I find it useful to add functionality to Gmail. (http://greasemonkey.mozdev.org/). I use the 'Gmail Macros', 'Gmail Label Colors', and Gmail Conversation Preview' scripts.
  • Broadband Speedtest and Diagnostics -- Check out your internet connection speed (http://www.gotomyhelp.com/forum/forumdisplay.php?f=18)
  • Gmail File Space (gspace) -- This extension allows you to use your Gmail Space (2 GB) for file storage (http://www.rjonna.com/ext/gspace.php)
  • Del.icio.us -- Manage your bookmarks independant of your browser; share links with your friends (http://del.icio.us/)
  • Google Notebook -- Clip and collect information as you browse the web (http://www.google.com/googlenotebook/overview.html)
  • DragDropUpload -- This extension lets fill an upload input of a form using the drag and drop service from the system (http://percro.sssup.it/~pit/mozilla/dragdropupload/)
  • CoLT (short for "Copy Link Text") -- copy a hyperlink's associated text in different ways (http://www.borngeek.com/firefox/colt/)