• Aardvark - web development. Isolate and modify individual elements on the page, right there in the browser.
• *Adblock Plus - get rid of banner ads, popups, and more, by choosing what servers to block.
• *Answers - look up unfamiliar terms from your browser with a right-click
• *ColorZilla - web development - figure out just what the codes are for a color in the browser, or enter codes and see a color
• Copy Link Name - so you don't have to try to highlight & copy that link without clicking it
• Crash Recovery - If Firefox should crash, Crash Recovery brings back up all your tabs when you start Firefox back up, so you haven't lost your place! After all, with all these extensions, your browser could get a little unstable.
• FirefoxView - Open Firefox with the current page or a selected link from Internet Explorer.
• FLST (Focus Last Selected Tab) - for tabbed browsing
• Forecastfox Enhanced - The new and improved version! Your forecast is in the status bar, along with current weather conditions and radar or satellite.
• FoxyTunes - Control iTunes from the status bar
• *Html Validator - web development. Icon in the status bar indicates whether your page is valid.
• *IE View Lite - Right-click to view a page in IE. (Silly non-cross-browser-compatible sites.) It looks like more people are using IE Tab now, but I haven't tried it yet.
• LinkChecker - checks links right on the page, highlighting them by color to show if they're good
• MeasureIt - measure elements in the browser - great for page template design.
• *Mouse Gestures - VERY handy for navigation. You remember how the scroll wheel freed you up from having to always move back to the scroll bar? This frees you up from moving to the back/forward buttons, the tab bar, and more!
• MR Tech Local Install - misc browser stuff. Sorts extensions, puts a "restart firefox" menu option, and more.
• Paste and Go - just like Opera. Right click in the address bar, and you'll have not only the usual Cut, Copy, Paste options, but also a Paste and Go option.
• Plain Text to Link (PTTL) - might not be needed with Mouse Gestures. Just in case some churl types an address but fails to link it.
• Screen grab! - Great for all those "You might want to print this out for your records" - keep it paperless! A step up from my erstwhile "Print screen, go to Paint, resize, scroll browser, print screen again, go to Paint ..."
• *TargetAlert - Don't leave "Home" without it. Puts a small icon by a link to indicate if it will open in a new window, is a PDF, is a link on that same page, is a mailto link, and more. Icon can either be part of the page itself, or you can just have it appear when you hover over the link. For the version that is compatible with FF 1.5 (not available on the Mozilla addons site), use this link.
• View Source Chart - web development. Might not need it if you have DOM Inspector?
• *Web Developer - the very most important web development extension! Too many features to list here. Just trust me.

Extensions I'd like to try:

• Console² - great for Javascript debugging
• DOM Inspector helpers - not sure of the finer differences between these two:
  • InspectThis - Inspect the current element with the DOM Inspector. Adds an entry to the context menu to open the DOM Inspector on the selected element.
  • InspectorWidget - Adds toolbarbutton (and context menus) for invoking the DOM Inspector (DOMi.) Clicking the toolbarbutton will enable to next mouse click on any chrome element to open a DOMi window with it positioned on the chrome element in the DOM tree.
• Regular Expression Tester
• Total Validator - Perform multiple validations and take screen shots in one go rather than using separate tools. Also performs accessibility validation, checks for broken links, spell checking, and takes screen shots so you can validate your pages with different browsers.
• XML Developer Toolbar - modeled after Chris Pederick's WebDeveloper toolbar