TheCoreWithin

The popular browser firefox isn't that great. At least not without the many plugins that make using it easier, faster, saver and more efficient.

Those are some of the ones I use:

Addblock Plus:
Blocks adds :)
https://addons.mozilla.org/en-US/firefox/addon/1865

NoScript:
Allows selective JavaScript permissions. A must have for security and privacy.
https://addons.mozilla.org/en-US/firefox/addon/722

CookieSafe:
Allows selective Cookie permissions. Just as NoScript, a must for privacy.
https://addons.mozilla.org/en-US/firefox/addon/2497

Internote:
Sticky notes you can attack to web pages. I think this could be useful, although I haven't found a use yet :)
https://addons.mozilla.org/en-US/firefox/addon/2011

TamperData:
Allows to intercept, change, and record communication with servers. Excellent for debugging.
https://addons.mozilla.org/en-US/firefox/addon/966

Bookmark Sync and Sort:
For all who have several computers, and a server, this addon allows to syncronize the bookmarks between the different installations, without having to trust a third party with them.
https://addons.mozilla.org/en-US/firefox/addon/2367

AutoComplete Manager:
Not only uses the history, but also bookmarks to auto complete your text in the address bar.
https://addons.mozilla.org/en-US/firefox/addon/2300