Oh Firefox, how I love thee. If only you launched a little faster on OS X. But I can’t quit you. Why? Add-ons!
del.icio.us Bookmarks – tag your bookmarks, access them anywhere, share with your friends.
Firebug – indispensable inline DOM visualization, and much more.
Web Developer – a ton of handy page hacking tools.
Aardvark – quickly clean a page up before printing
DownThemAll! – download accelerator and easily fetch all embedded links of a given file type in one go.
Fasterfox – page render time, network speed tweaks, and pre-fetching.
iMacros – page scripting, automation, testing, etc.
My new favorite: Copy All Urls
addons.mozilla.org/en-US/firefox/addon/934
Great for opening some tabs and copying the titles and urls to send in an email or text file!
Also YSlow is a great performance review tool for optimizing your website or web application:
addons.mozilla.org/en-US/firefox/addon/5369