• Web Developer Extension My personal fav. Adds an extemely useful web developer’s toolbar with a multitude of features.
• IE View Lite Allows the current page or selected link to be opened in IE.
• Adblock Plus Goodbye annoying adverts! I use it in conjunction with the Adblock Filterset.G Updater.
• Performancing for Firefox Make posts to most popular blog software,right from your browser. Nice.
• No-Referer Open a link in a new tab without sending the referrer information.
• Image Zoom Control sizing of images with your scrollwheel and/or menus.
• Download Statusbar View and manage downloads from a tidy status bar.
• UnPlug Grab plugin media from sources like Youtube or Google Video.
• Flashgot Queue files to your download manager and more.
• Gmail Notifier This one should be self explanatory.
• FoxyTunes Control your music player of choice from within Firefox. I’m also using the FiRemote FoxyTunes skin.
• ColorZilla Advanced colour picker. Handy!
• Tabbrowser Preferences Extend the functionality of tabbed windows.
• BugMeNot Uses Bugmenot.com to bypass compulsory registration.
• Paste and Go Paste a URL and load it in one click. Why this isn’t standard functionality is beyond me.
• Stop-or-Reload Button Combines the Stop and Reload buttons into one, Safari style.
• SearchStatus Get search engine info for pages as well as Google pagerank and Alexa ranking.
• Linkification Converts plain text URLs and mailto links to a hyperlink. Great for the lazy.
• Update Notifier Checks for updates to your installed extensions and themes.
• HTML Validator Check the validity of your code with this great extension. Adds an indicator to the statusbar.

For the curious, I’m also using the Qute 3.1 theme on Firefox 1.5.0.4.