I've added so many extensions to my Mozilla Firefox browser, it's literally unrecognizable! It's amazing how modular a browser can be, allowing users to fit-in only those pieces that they need to help fine-tune it. All the things I could have hoped for in a browser are available via extensions. My only gripe is that the industry still builds sites keeping only IE in mind. Thankfully, the archaic mindset is changing. Even Yahoo! Videos are now Firefox compliant.
Addendum: I've just learnt that tabbed-browsing in Firefox supports drag-&-drop! Let's see IE doing that!