This is an update of my previous list of Firefox 1.5 Extensions.

I’m a long-time user of the Mozilla and Firefox browsers. The base feature set is amazing but the extensions are what really make this browser a requirement. Here are my favorite extensions: Required (I use constantly):

• Tab Mix Plus: If I had to choose only one extension, this would be it. It makes the tabs behave any way you want them to behave. I use it to make child tabs open beside their parent, for the title text to be blue when the tab is unread, to show page download status in the tab title.
• AutoFill Forms: Tired of continually filling in the same info over and over again? This extension allows you to add a button to your icon bar. When you click it, it will auto-complete the common form fields on the currently-displayed page.
• Copy Plain Text: Will not copy formatting when copying text. Prevents the need to do an Edit / Paste Special / Plain Text command in the destination application. Can be set as the default copy option and optionally removes excess whitespace. I use this on every time I copy from my browser now.
• Download Status Bar: A great replacement for the annoying download window that pops up. Less obtrusive and it give the user a bunch of options to make downloads behave how ever you want them to behave.
• DownThemAll: A download manager built inside of Firefox – no external programs to worry about.
• FasterFox: Automatically modifies settings to speed-up Firefox.
• IE Tab: Can switch the current tab back and forth between IE and Firefox, all within Firefox. Great for sites that don’t support Firefox and for page design validation.
• Link Alert: Displays an additional icon by your cursor to let you know if a link is an e-mail link, external site link, java script, office document, PDF, etc. Great to prevent the opening of unexpected files.
  
• OpenDownload: Gives you the option to download a file to a temp location and launch it to the default Windows application. This is perfect for program install files that you don’t want to keep, so you don’t have to download install files to your desktop, run the installer, and then delete the file. Plus, it will automatically delete the temp downloads a few days later. This is similar to a feature offered by IE, one of the very few IE features I miss.
• PDF Download: Asks you how to handle a PDF: view in browser, open in external viewer, or download. Prevents those frequest lock-ups I had from acrobat crashing inside of Firefox.
• QuickJava: Disable Java and Javascript quickly, in case you visit a suspicious site that you suspect may be running suspicious code.
• Remember Mis-Matched Domains: If you frequent web sites / servers that have self-generated security certificates installed, you’ll always get a security pop-up. This extension allows you to ignore that message for specified domains.
• Smart Middle Click: I love using the middle mouse button to open links in new tabs. Unfortunately, some sites don’t use conventional links and instead use javascript to link to the new page, resulting in a blank tab instead of the page you’d expect. This extension resolves that problem.
• Update Notifier: The best way to see when there are updates to Firefox and any extensions.
• URL Fixer: Fixes the common typos people make when typing a URL in the location bar (such as .con -> .com); fixes about every common mistake you could make.
• Firefox Extension Backup Extension: backs-up all extensions, preferences, and bookmarks (for Windows and Linux)
• These aren’t really extensions, but be sure to check the Additional Toolbar Search Engines page (I added Wikipedia and IMDB.com)
• MozBackup: This stand-alone program (not an extension) backs-up everything in Firefox and Thunderbird (Windows only)

Website-Specific Extensions:

• Amazon S3 Firefox Organizer (S3fox): If you use the Amazon S3 backup service, this is the easiest way to manage bins, change share permissions, and upload/download files.
• Kaboodle.com Add Item to Wishlist: Kaboodle.com seems to be geared toward young women, which does not classify me. Oh well, it still offers the best central wishlist features of any site I’ve found, using a clean web 2.0 approach.
• MyTimeZone for Ebay: If you don’t live on the west coast, or if you don’t like to read times in the 24-hour format, this extension is for you. It converts the times on Ebay listings to your local time zone, so you don’t have to perform math to determine when an auction ends.
• Verizon Wireless Minutes Used Extension: Don’t you hate it when you use more minutes than your plan allows? This extension allows you to track the number of minutes used during the current period and display it along the bottom in the Firefox info bar. Also available for T-Mobile.

Recommended for a Work Laptop:

• LeechBlock: Find yourself checking the news too often? LeechBlock will let you know when you’ve passed your own pre-set threshold.
• Quick Proxy: Quickly turn the proxy on and off. Great for your work laptop. (Replaces Proxy Button)
• User Agent Switcher: At work, you are more likely to run into a website that thinks it requires IE to function properly. This extension allows Firefox to temporarily trick the server into thinking it is IE, eliminating the “You must be using Internet Explorer to view this site” message.
• Webmail Compose: Integrates webmail in case you don’t have Thunderbird or any other mail client installed on that machine. Great for your work laptop if want to send an e-mail from your personal account rather than your work e-mail application.

Lightly Recommended (I use occasionally):

• Xinha Here!: Lets you launch a client-based WYSIWYG HTML editor. Uses the Xinha editor, but I would prefer TinyMCE or FCKeditor.
• Mozilla Labs Weave: great for bookmark backup, but there is so much more it can do beyond that.
• Colorzilla: If you do any web design, this is great for figuring out which colors are used anywhere on a page.

Old & Obsolete or “Still On the Fence” (but I’m listing them anyway):

• Adblock Plus + Adblock Filterset.G Updater: Great for removing unwanted ads in web pages; auto-updates the blocked sites list. However, if everyone used this extension, no websites would earn revenue from ads and would go out of business. So I no longer use this extension.
• del.icio.us: Not sure I get to popularity of this site, but it allows a user to mark, save, and share interesting web content.
• Flashblock: Disable Flash animations until you give them permission to run, to disable many of those annoying advertisements. Sounds like a great idea, but this extension block way too many things and wouldn’t unblock them. So I uninstalled.
• IE View or IE View Lite: Since switching to IE Tab, I don’t use these two. However, I do respect their small size and simplicity. These two programs let you open the current page in Internet Explorer (useful if case the web page author does not properly support Firefox).
• StumbleUpon: Helps you find new sites that match your interests.

One must-have utility for backing-up setting prior to a reformat or computer switch is MozBackup.

Links to other Extension Lists:

• The most popular extensions on the official Firefox extension page
• Security extensions
• 25 Extensions you didn’t know you needed
• List of Extensions recommended by Google engineer
• List of almost-necessary extensions
• Download.com extension lists: Vol 1, Vol 2, Vol 3, User Favorites
• Mozilla.org recommended extensions
• Top 10 Firefox Extensions to Improve your Productivity