Greasemonkey!! "Always on"
-My favorite by far and the amount of scripts made for it is insane.

Open With Photoshop! "Always on"
-Very useful since I'm a Ps junkie.

Adblock Plus "Always on"
-I hate ads!

Menu Editor "Always on"
-Lets you edit your context menus as well as your main tool menus.

Element Helper "Always on"
-It's nice but I had to edit my own script to make it better to use with one click.

Firebug "On when needed"
Very handy!

No Script "Always on for sites I don't know."
InspectorWidget "On when needed"
-Nice for scripting.

Foxy Proxy "Always on"

All in one gestures. "Always on"
Yup I'm lazy.

Tabmix Plus "Always on"
-My tabs MY WAY!

All in one sidebar "Always on"
-Pop out bar on mouse hover or click.

Hide Caption Titlebar Plus "Always on"
-Cuts the bars down to a small icon till you hover over it.

No squint site settings. "Always on"
-Nice for custom page colors. "Yeah I know stylish is better but I like NSSS better."

Remove It Permanently "Always on"
-The adblock element helper makes this one useless but I still keep it.

LastPass "Always on"
NewScrollbars "Always on"
-THIN SCROLL BARS

PageZipper "Always on"
-F you next page button!

ProxyFire "Always on"
-A quick proxy switcher that comes with their software I use it with proxy goblin only because it checks the list better.

CoolPreviews "Sometimes"
QuickJava  "Always on"
-Lets you disable Java,Javascript,Proxy,Flash,Silverlight,Cookies,Images,Animated Images and CS styles.

FVD Speed Dial  "Always on"
-I use it as my home page since it helps me keep track of my bookmarks very nicely.

TLDR: Too Long Didn't Read "Always on" (It kicks as when you don't have time to read a full page.)
-Reads the page for you and gives you a summary and surprisingly it's very damn accurate.

Rotate Image "Sometimes"
DownThemAll! "Always on"
-Goodbye internet download manager.

User agent switcher "When needed"
-Some guys like to dress up as chicks but I like to dress up as Google.  :P