Links

I like these…

del.icio.us Bookmarks extension
searchOnTab. This extension allows users to select where are loaded the results of the search bar.
Colorful Tabs. Colors every tab in a different color and makes them easy to distinguish while beautifying the overall appearance of the interface.
Download Statusbar
Tree Style Tab
It’s All Text!

Development

To try…

http://readitlaterlist.com/ Save pages to read later…
HttpFox, An HTTP analyzer addon for Firefox.
DZone Voting
FaviconizeTab
Adblock Plus (recommended by Tony Fuller).
http://www.icyte.com/ iCyte enables you to highlight and save text on any webpage.

Not too keen on these:

ColoUnREaDTabs. Marks unread tabs in red-bold-italic allowing to easily identify them.
Operator Operator leverages microformats and other semantic data that are already available on many web pages to provide new ways to interact with web services.
Allows JavaScript and Java execution only for trusted domains of your choice.
PDF Download
Foxit PDF Reader
TwitterFox