Just those add-ons I think sound interesting enough to try some time.
Personas are free, easy-to-install "skins" for Firefox. Personas Plus extends that built-in functionality to give you even more control and easier access to new, popular, and your own favorite Personas.
Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...
View HTTP headers of a page and while browsing.
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
Skips unnecessary pages on sites like Rapidshare, 4Shared, zShare, Mediafire, and more. Try it out, or watch a demo at http://www.skipscreen.com
Why click through ad-laden pages and wait for countdowns when your computer can do it for you
Stop secret tracking of your web browsing.
See video: http://www.abine.com/preview/taco.php
Keep your personal info private on the web with new & powerful privacy tool, MaskMe.
Drupal for Firebug extends the Firebug module to provide Drupal specific debugging and status messages. The 2.0 version doesn't work, until 2.1 is approved by mozilla, we recommend Downloading straight from the Project's Repository page.
Switch tabs by scrolling with the mouse wheel in the tab bar.