Recommend Good Firefox extensions for developers? (I'll show you mine if you show me yours...)

[eluser]Unknown[/eluser]
Hi! I wanna share mines and see if yours could help me to be more productive.

The ones I usually use are:

Cookiepie: to have multiple independent sessions/cookies on each tab. [by Me and Sebastian ]
Firebug: to debug javascript, CSS and AJAX calls.
TamperData: to debug Post, Gets and cookies.

I want to hear about yours now