I have not tried all of these add-ons out, but if you see something you like, great!

I got these all out of a magazine called Practical Web Design which is based out of the U.K.

If you are serious about web development, I would highly recommend this magazine.

Aging Tabs

http://addons.mozilla.org/firefox/3542

Tabs you’ve looked at recently appear in bright colors, those you haven’t go dark.

All-in-One Gestures

http://addons.mozilla.org/firefox/12

Enables you to navigate by waggling the mouse, scrolling the mouse wheel and using the rocker switch. A huge time saver.

All-in-One Sidebar

http://addons.mozilla.org/firefox/1027

If you like Opera’s sidebar, but prefer to stick with Firefox, then you will want this. Once installed, it gives you a panel on the left or right side of the browser window which you can use to switch between each browser’s features

Blue Organizer

www.adaptiveblue.com

Cross between a search tool and an information organizer. It’s kind of like bookmarks that enable you to add tags, give a URL a rating our of five, add a description and add them to the bookmarking service of your choice

Browster

www.browster.com

This plug-in adds a live page preview to search results which makes it a powerful ally in the fight against search engine spammers and other dishonest types. (I have this installed on my computer, and it takes a little getting used to, but it is a nice feature to have.) Warning, it works on every link!

Clipmarks

http://addons.mozilla.org/firefox/1407

Handy research tool tht enables you to highlight and save bits of web content such as article exerpts, quotes or images. The clips are stored at the Clipmarks site

Delicious Bookmarks

http://addons.mozilla.org/firefox/3615

Official Yahoo plugin replaces Firefox’s standard bookmarks.

Drag de Go

http://addons.mozilla.org/firefox/2918

Another time saver. It enables you to do useful things by dragging text, links or images. Depending on the direction in which you drag, and the options you choose, it will execute things like opening a link, searching for the selected text, saving the selected item or viewing the page source.

ErrorZilla Mod

http://addons.mozilla.org/firefox/3336

Replaces the default 404 page with something more useful that enables you to retry, check Google’s cache or the Wayback Machine. It also let’s you carry out network tasks like ping or trace, and WHOIS.

FasterFox

http://fasterfox.mozdev.org

Fasterfox makes your browser prefetch links, blocks flash plug-ins, or shows how long pages are taking to load.

GTDGmail

www.gtdgmail.com

Getting Things Done attempts to make Gmail more useful by adding GTD-related labels and reviewing options with tasks and reminders.

ScrapBook

http://amb.vis.ne.jp/mozilla/scrapbook

A quick and effective tool for anyone who uses the web for research. ScrapBook enables you to store web ‘clippings’ in the same way you would organize bookmarks or images in a scrapbook!

StumbleUpon

www.stumbleupon.com

Looking for inspiration? StumbleUpon takes you to a new web page based on other users’ recommendations and your feedback on it’s choices. Most add-ons are great time savers, this one is a great time waster!

Tab Mix Plus

http://addons.mozilla.org/firefox/1122

Gives you more control over the way Firefox handles tabbed browsing. You can specify how links should be opened, how they look, what appears on the tab context menu and what order the tabs appear in.

ColorZilla

www.iosart.com/firefox/colorzilla

Photoshop’s eyedropper tool in your browser

FireBug

www.joehewitt.com/software/firebug

Provides tools for poking around page code and includes a JavaScript/CSS error console, a code debugger, Ajax traffic logging and a code inspector

Greasemonkey

http://greasemonkey.mozdev.org

There are more than 2 million Greasemonkey scripts at http://userscripts.org ranging from scripts that bypass download sites’ “wait 30 seconds” systems to adding extra file types to Googles’ advanced search.

IE View

http://addons.mozilla.org/firefox/35

With the press of a button, you can check to see how IE visitors will be viewing your site.

User Agent Switcher

http://addons.mozilla.org/firefox/59

For as long as developers use a browser sniffer that block non IE browsers, then this add-on will be a necessary part of any self respecting web browser’s toolkit

View Dependencies

http://addons.mozilla.org/firefox/2214

The View Dependencies add-on sticks an extra tab on the page info window that enables you to see all the files loaded by the current page, grouped by category for easy identification.

AdBlock Plus

www.adblockplus.org

Gets rid of most online ads without any tweeking, but if an odd one sneaks through, you can block it with a single click

BugMeNot

http://roachfiend.com/archives/2005/02/07/bugmenot

Ever clicked on an article and the site expects you to hand over your entire life story? BugMeNot gives you other people’s login details so you can read stories without first having to provide your own.

Forum Fixer

http://addons.mozilla.org/firefox/3267

This add-on strips giant avatars, off-site images and silly signatures from sites whose url contains the word “forum” or “vbulletin”

ImgLikeOpera

http://addons.mozilla.org/firefox/1672

Good for dialup users. ImgLikeOpera enables Firefox to treat images in much the same way that Opera does. Example: Block third party images.

NoScript

http://addons.mozilla.org/firefox/722

NoScript disables Java and JavaScript for sites that don’t need to use them, and it uses a whitelist, so you don’t lose functionality on the sites you know are safe.

PDF Download

http://addons.mozilla.org/firefox/636

Have more control over PDF’s: Save them to disk, open them immediately or view their contents in good old fashion HTML

Remove it Permanently

http://addons.mozilla.org/firefox/521

One-click deletion of things you don’t want to see ever again.

CoComment

www.cocomment.com/tools/extension

View all of your online conversations in one place. Good for blogs and sites such as Flickr.

Deepest Sender

http://addons.mozilla.org/firefox/1811

Originally designed for LiveJournal, Deepest Sender enables you to update WordPress and Blogger blogs using it’s own post editor

Live Writerfox

http://addons.mozilla.org/firefox/3214

If you use Windows Live Writer to compose your blog posts, this add-on enables you to send links or text from Firefox to WLW. Doesn’t work on a Mac (Sorry Mac users!)

Performancing

www.performancing.com

Blog editor that works on all major blogging platforms, supports trackbacks, Technorati tags, and Delicio.us, and can handle multiple blog accounts

Resizeable Textarea

http://addons.mozilla.org/firefox/3818

If online forms don’t provide enough room for you to breathe, this nifty add-on enables you to make text fields bigger

Sage

http://sage.mozdev.org

Turn Firefox into a fully fleged, multi-pane newsreader with CSS based layout, multilingual support and full integration with your browsers Live Bookmarks. Yes, Firefox can still handle RSS feeds but Sage does it better!

CookieSafe

http://addons.mozilla.org/firefox/2497

CookieSafe expands on Firefox’s existing cookie control system to give you some extra options. With this extension enabled, you can see what cookies a site is trying to install and where they came from.

hideBad

http://addons.mozilla.org/firefox/1052

Saves all the currently opened tabs, closes them and replaces them with something less likely to land you in trouble. It can also clear any incriminating traces, which can be handy if you are using the office PC to look for another job!

TrashMail

http://trashmail.net

Protect yourself from spam with TrashMail’s instant disposable email address. Incoming messages will be forwarded to your real email account until the time you specify.

AllPeers

www.allpeers.com

An easy to use P2P system. And it all happens in your browser. Sharing with friends and colleagues is as easy as dragging and dropping

Download Statusbar

http://downloadstatusbar.mozdev.org

Instead of confining downloads to a separate window, Download Statusbar sticks them in a bar at the bottom of the browser window which hides when it’s not in use.

DownThemAll

www.downthemall.net

Download every linked file or image from a page with a single click and do it quickly. DownThemAll is a download accelerator as well as a download manager, and it can download from multiple locations simultaneously for maximum speed.

Fast Video Download

http://addons.mozilla.org/firefox/3590

Enables you do download embedded video from sites

FireFTP

http://fireftp.mozdev.org

An FTP client that includes directory synchronization, SSL encryption, and file hashing. Donations go to deserving charities.

FlashGot

www.flashgot.net

This is a standalone download manager.

Gmail Space

http://addons.mozilla.org/firefox/1593

Allows you to use Gmail space as hard disk space. Basically it’s an FTP client.

 Well, that's all for now... Enjoy!

I did not notice in your list the ForecastFox plug-in.  This plug-in puts items along the bottom of the browser window for the weather.  It is very customizable.  You can have just the current forecast or multiple days out.  You can show day, night, or both day and night.  There are a lot of other things that you can add to each day as well.  It primarily depends on the amount of screen real estate you have side to side for your browser window.  This is way better than weather bug or any of the other resource draining tools most people use.