If you use FireFox on a daily basis, no doubt you have your own list of favorite add-ons. But who has the time to constantly be on the lookout for new ones? So, this list was put together for anyone who does business online and needs tools to help you be more efficient.
The Top 10
1. InFormEnter
What it is: When you turn it on, it adds a little
button next to all the form fields on a web page. Clicking the button pops up a list of all the phrases you’ve saved:

Why you’ll like it: It’s a great time saver for any web forms requiring name, address, email, product description – you name it.
Link: https://addons.mozilla.org/en-US/firefox/addon/673
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2. ScrapBook
What it is: A tool that takes snapshots of the current web page. You can organize your scrapbook items in folders and access them through the menu or a sidebar:

Why you’ll like it: From a business perspective, it’s good for recording receipts of online purchases. Plus the edit page capability allows you to erase elements, making it easy to clean up a page for printout.
Link: https://addons.mozilla.org/en-US/firefox/addon/427
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3. Firefox Extension Backup Extension (FEBE)
What it is: This extension allows you to save all your FireFox data, including passwords, bookmarks, themes, extensions, preferences, and more:

Why you’ll like it: If you do enough business on the internet, eventually your find that a lot of mission critical information is stored in your browser. Backing up this data becomes crucial.
Link: https://addons.mozilla.org/en-US/firefox/addon/2109
[Note, this extension has a companion extension – CLEO that will combine all your extensions into a single .xpi file for easy reinstall: https://addons.mozilla.org/en-US/firefox/addon/2942]
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4. ViewMyCurrency
What it is: A tool that will convert any amount on a page to your selected currencies. Click the status bar button
and any currency values found on the page will be changed, as the following before and after pictures show:

Why you’ll like it: This is probably more useful for those outside the U.S., but it’s handy for anyone that wants to save themselves a trip to www.xe.com to get convert prices into your local currency.
Link: https://addons.mozilla.org/en-US/firefox/addon/1854
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5. WorldClocks
What it is: A tool that shows you the current day and time for selected cities around the globe. Clicking on the status bar display, it pops up a list of all the cities you’ve added. You can either use the built-in list of cities or set up your own.

Why you’ll like it: It’s great for figuring out when someone halfway around the world is likely to be at work.
Link: https://addons.mozilla.org/en-US/firefox/addon/3010
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6. Fetch Text URL
What it is: A tool that allows you to right-click on a non-linked, text URL and fetch it in a new tab.
Why you’ll like it: It saves you added typing.
Link: https://addons.mozilla.org/en-US/firefox/addon/518
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7. SearchStatus
What it is: A SEO tool that sits in your status bar. You can see the Google Page Rank and Alexa rank, and you can access the robots.txt, archive.org (aka, Wayback Machine), and whois of the current site via the popup menu.

Why you’ll like it: Unlike other SEO toolbars, it’s unobtrusive and provides quick access to information.
Link: https://addons.mozilla.org/en-US/firefox/addon/321
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8. RankQuest SEO Toolbar
What it is: A full featured SEO toolkit (accessible via toolbar or context menu) that provides a number of analysis tools for webmasters. Included are speed test, a lynx viewer (how does the Google bot see your page), meta tag analysis and generator, keyword density analysis, text ratio calculator, and many more tools.

Why you’ll like it: It packs a lot of tools into a single toolbar. But, toolbars take up page space so this one is better off hidden most of the time, and SearchStatus (above) is more convenient for day to day info.
Link: https://addons.mozilla.org/en-US/firefox/addon/1471
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9. Web Developer
What it is: A toolbar with a wide assortment of tools to provide you with info about the current page. It has too many features to cover here. The snapshot below left is the information panel shown when clicking on any page element. The snapshot below right is an example of the CSS editor (in this case, in the left sidebar).

Why you’ll like it: This list is for Internet Entrepreneurs, not web developers, but this is a handy tool for anyone who owns a web site. It’s helpful for debugging CSS layout problems. Added bonus, too many sites today think it’s cool to have low-contrast text. No problem. With the Web Developer toolbar you can simply identify the element containing the text and then edit the CSS in the side bar and have the page style updated instantly.
Link: https://addons.mozilla.org/en-US/firefox/addon/60
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10. PwdHash
What it is: An automatic password generator.
Why you’ll like it: Security, security, security. With this tool, there’s no excuse for using the same easy to remember password for forums as you would for your online banking account.
Link: https://addons.mozilla.org/en-US/firefox/addon/1033
[Note: The author of Allow Right-Click, listed below, also has an "Always Remember Password" add-on that lets FireFox save passwords for sites that normally don't allow it: http://roachfiend.com/archives/2005/03/03/always-remember-password/]
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5 Honorable Mentions
Yoono
What it is: A sidebar toolbar that shows related web sites for the one you’re currently on.
Why you’ll like it: This is incredibly handy for both topic research and seeking out sites for back links.
Link: https://addons.mozilla.org/en-US/firefox/addon/1833
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Allow Right-Click
What it is: Overrides any web scripting that disables right-clicking your mouse and getting the context menu.
Why you’ll like it: If deal with web pages (or control panels) that disable right-clicks, this add-on will let you context menu item.
Link: http://roachfiend.com/archives/2005/03/03/allow-right-click/
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Image Zoom
What it is: Right-click on any image and zoom in via the context menu.
Why you’ll like it: Bigger is sometimes better.
Link: https://addons.mozilla.org/en-US/firefox/addon/139
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IE View
What it is: Opens the current page in Internet Explorer. (Note there is also IE Tab add-on, which runs IE in a FireFox tab. Both work equally well.)
Why you’ll like it: Some websites are still operating in IE only mode. This tool will make swear at the screen less.
Colorful tabs is a very good extension that ads a good visual organization to your browser by color coding the tabs.
Thanks for introducing Web Developer plugin to me. I like it very much.
Fetch Text URL is pointless … Linkification is all you need
I just tried Linkify. It doesn’t work on links that are just “domain.com” without the http, www, etc. I use Fetch Text URL for that more than anything.
FireFox 3 Updates:
I had the same issue regarding View My Currency and found Forex Currency Converter as a replacement. Quite handy; I would recommend..
https://addons.mozilla.org/en-US/firefox/addon/7908
View My currency is now maintened under another name, convert my currency,
http://converter.mozdev.org/ConvertMyCurrency/