Some FireFox plugins/ addons which I use often....

[sebastian]

More... - weather addon with a cool animated satellite/radar combo images


More... - Shows Alexa and G page rank and quick access to other domain info


More... - needs no intro


More... - split browser, good for widescreens.

 

[tongyun]

The things that I really like about Firefox are the same things that drive me‌ crazy. Because I have so many cool add-ons, it takes FireFox a bit of time‍ to load, but it's better than IE.

 

[rajiu]

I love the new add on called the personas for firefox where you can design‌ the themes of your fire fox almost everyday and its easy to do with less‍ time

 

[julijuli]

I like nodofollow plugin. It let you easily identify which link is nofollow and which‌ one dofollow.

I also like firebug Plugin. It helps you a lot on designing your‍ website.