I had no idea that there were so many extensions (there are over a thousand of them) and new ones are posted everyday. These extensions make Firefox the digital analogue of a Swiss army knife, allowing the user to do much more than just surf pages. Not only is there a plethora of extensions, the quality is pretty good. I stumble across a new Firefox extension every few days. A script I came across today in fact is a blogging tool from Performancing that integrates with all of the major platforms and allows you to write and save posts before publishing to your blog.
Some Firefox Extensions that I couldn't live without:
list of extensions they use and think are noteworthy. If you find Rijk's page too noisy to read, you can always use Mozilla's Firefox Extension Database which has an excellent interface for finding the extension you need. Here is the link to the Firefox Addons website.