Alright here is a list of the plug-ins I live and die by on Firefox:

1-click weather
I like this better than forecasterfox

adblock plus
Keep all those pop-ups and banner ads hidden automatically updates with new bad stuff

User Agent Switcher
This allows you to change what the webserver sees your browser as this helps you with those sites that block Firefox.

Auto Copy
Just select the text and it gets copied to the clip board

autoHideStatusbar
Auto Hides the status bar to give you more room

Copy Plain Text
Works with Auto Copy so that when the text is selected it just copies the text not the formatting

Download Statusbar
Clean up that damn download menu and makes it a nice toolbar on the bottom auto hides when not in use

FireFTP
Nicely integrated FTP client

Fission
Adds the loading bar as the background to the address bar. (Safari thing)

MediaPlayerConnectivity
Lets you choose the media player to play rich content (great for linux)

Mouse Gestures
Turns your two button mouse into a super navigator

Tab Mix Plus
Adds tab features and options

Tiny Menu
Shirks menu bar to just one link so you can consolidate everything to one line

TinyURL Creator
Right click and create tiny URLs to links or current pages great for compacting long URLs for emailing the fam or anyone

IE Tab
Of course IE Tab for those sites that have issues with firefox