Firefox extensions that aid website design

Firefox is widely used by designers. I have reviewed some of the most useful firefox extensions for website design. You can read about them here.

Here are original Firefox extensions on Mozilla home page.
Examples:
-some uncommon Dictionaries (Hungarian, Czech, Ukranian...)
-Mouse Gestures: you make orders with quick mouse moves
-Video downloader: you can DL videos from about 60 video sites directly (YouTube, Google and Yahoo videos, Metacafe, iFilm...)
-Table tools, released today...
and many more.

Firefox's best feature is its customizability through extensions and skins. You can't do that with any other browser except Firefox and Seamonkey.