All of these extensions can be easily Flock’d, so this applies to Flock too.
There are SOOOOO many top 10 Firefox Extensions lists out there. So I’m now going to make MY OWN Top 10 Firefox (and Flock) Extensions list just because I feel like it.
1. IE Tab
An essential extension for just about anyone. Even though most websites now work in both Internet Explorer and Firefox, this can really help when you need to see how a site looks in different browsers - while still in Firefox! Basically, IE Tab lets you open websites in a new tab, and that new tab is like a portal to IE, but inside the Firefox interface!!!
2. FireFTP
Not essential for everyone, but this is a very useful FTP program inside of Firefox. It saves you the extra hassle of buying one that turns out it’s only a demo after 30 days, and then you can’t do anything anymore (this is completely free.)
3. StumbleUpon
This isn’t really a tool, it’s actually more of a website and toolbar. Discover new websites as rated by users like you, choose your categories and all of the sudden 2 hours have past. Whoops. (It’s a HUGE time waster.)
Gmail Manager sits on your toolbar and notifies you when you have new mail, at a predescribed time frame. There are a lot of different Gmail extensions for Firefox. Personally, I like Gmail Manager because it allows you to manage multiple accounts at once.
5. MeasureIt
I couldn’t live without this simple extension. It sits in your browser, and when you click on it’s little icon, it allows you to measure the pixels of anything on the current page. So if you need to know what the width of the page is, you just click and measure. It’s sort of like using a ruler digitally - only it’s more fun.
6. Highlighter
I find this especially useful on long boring pages about the conflict over water in the Middle East. It lets you (digitally) highlight (and choose the color) any text on the page. One problem is you can’t easily un-highlight stuff. Still, it’s a great tool.
7. FoxyTunes
Allows you to control almost any and every media player in existence from the comfor of the lower-bar-thing. Very customizalbe and easy to use, although a bit slow.
8. Screen grab!
Simple screenshot taker. Right-click > Screen grab > Save. And you’re done.
9. Greasemonkey
Allows you to customize scripts, doing all sorts of fun stuff. Even allows you to take the ads out of Google.
10. Non-existent
One of the reasons why I switched back to Flock is because I couldn’t find a one-click-bookmark extension for Firefox, like what Flock has with the star. You just click it, it turns from blue to orange, and you’re done. It’s so easy. No title and description, and putting it in a folder - just one click. If someone knows of an extension that does this, please tell me although I’m not gonna swith back just because of that.

The Firefox extension I can’t live without is Google Browser Sync, since I use multiple computers. It goes beyond Safari’s .Mac sync by also syncing open windows & tabs, cookies, and saved passwords as well as bookmarks. It can even sync between Mac, Windows, and Linux versions of Firefox.
Also, Video Downloader, which lets you easily save videos from YouTube, Google Video, etc.
I no longer use Gmail Manager; instead I now use Google Notifier, which lives in my menu bar.
I also can’t live without Google Browser Sync, as I have a Mac at home and PC at school and need that syncing. Also, I on’t use Flock because a) Firefox is more matured, b) I can change the theme of Firefox, c) I don’t need Flock’s RSS reader and blog editor (I have NetNewsWire and ecto), and d) I can get an optimized build of Firefox for my Mac’s processor, which has Mac-style buttons.
Here’s my take on your extensions:
1. On PC, it’s cool. It doesn’t exist on Mac. Oh well.
2. On my laptop I use it, but I have CaptainFTP on Mac, though I want Transmit.
3. I got bored with it pretty quick. Maybe I should hide the toolbar.
4. I’ve swirched from Gmail to my own, hotsed mail.
5. Sounds cool for a web developer, but pretty pointless for a normal person.
6. Sounds cool.
7. I don’t use it becuse my keboard has multimedia controls on it.
8. OS X has the built-in capability to take screenshots (either a selection or the whole screen) directly to a .png or to the clipboard.
9. Greasemonkey rules!
10. I don’t care about one click bookmarking.
@Aaron:
Here’s my take on your take on my extensions:
1. No comment.
2. Doesn’t matter
3. I keep the toolbar hidden unless I use it - I don’t like the fact that it’s a solid toolbar (you can’t move the buttons around to the other bars.
4. I don’t understand why - but uhuh.
5. Are you saying I’m a web developer???
6. It is
7. Mac (sorta) alternatives
8. More Mac alternatives
9. No disagreement there
10. ??????!!!!!!! You are a crazy man, a craaaazy man.
@Mike:
VideoDownloader is cool, but I don’t usually want to download videos from YouTube (of course, that’s just me.)
@Aaron:
There’s a little sitcheroo thing going on here - I remember when we both thought the opposite….