1. Bookmarks Toolbar Folder 2. Adblock/Flashblock 3. Scrapbook Can't imagine using a browser without these features.
i hate explorer, but i like it better than firefox. i prefer opera which has more features than firefox, and seems easier to use for me. maybe cause i use it for so long now.
If you still want to use the IE engine but add some nice features such as tabbed browsing, popup blocker, etc., try something like Avant Browser.
check out IE7 beta 2, downloadable from MS website - has all of the raved about features of firefox mentioned above and improved tabbed browsing. Still in a beta for now (on XP) and apparently only to be released mainstream for windows Vista / XP64, but the features are sweet and i'm enjoying using it, much better than Firefox which i was using before. http://www.microsoft.com/windows/ie/ie7/default.mspx
I have heard the the biggest advantage to Firefox is security. IE is supposedly ripe for invasion of viruses, adware, spyware and other serious intrusions.