IMHO:

1. AdBlockerPlus

2.AutoPager

3.NetherWeb

1. Download Statusbar
2. NoScript
3. IE Tab

1. Developper toolbar
2. IE Tab
3. Search status (Google page rank, alexa rank)

I'm a Web programmer/designer so those are very useful for me.

What is NoScript? IE Tab? I'm assuming the download status bar is just showing the download status on your current window and tab instead of the new window for downloads?

IE Tab is to see your page as they would appear in Internet Explorer without having to start up IE and type the address. The reason I need this is because IE does things it's own way and will interpret HTML and CSS in a different way than Firefox or most other browsers. When creating a Web site, you have to make sure everyone will see the same thing regardless of their browser.

Download Statusbar adds a status bar to the bottom of your window to display downloads. I hate the new window thing in FireFox.

NoScript blocks any script that I don't allow. This helps prevent cross site scripts from running and installing viruses on my machine. Without NoScript, Firefox isn't all that much better than IE if it is properly configured. NoScript provides security and abitlity to not disable every script on the internet at the same time.

IE Tab allows you to use the Internet Explorer engine to render the website. Ever browse in FireFox and run across a website that is IE compatible only? IE Tab allows you to click an icon on the bottom of FireFox and that tab only switches to IE. It is rather handy.

Yeah. IE Tab is great. Most websites run fine in Firefox but there are many more professional (for lack of better word) websites that just don't work in Firefox so you need IETab.

And as far as I'm concerned, NoScript should just come with FireFox.

The downloading thing I don't really care too much about since I don't really download things very often or more than one thing at a time.

That's a weird thing to say. To me if a site is professionally done, it will run fine in all main browsers.

Like I said, I can't think of the word at the moment and I can't remember the particular site I started using IETab for.

I'm not talking about professionally done sites or sites made by a professional, I'm talking about sites you might use in the office like certain webmails and online task management systems.

For example, our university student class signup/management portal forced you to use IE for years. That is what originally got me hooked on IE Tab.

As for the download bar, I download hundreds of images/zips/boxarts each week for the game database here at VGChartz so it is extremely useful.