Waiting for a stable version of IE8, I'm installing the latest version of IE7Pro, the definitive IE7 Plug-in.
Of course with Firefox Extension you can get a better customization, but I think that for a IE user this is a must have. It adds features and just works without any issue.
Personally I appreciate most the possibility to change the proxy settings with two click, have a real download manager plus a whole set of useful customizations.
What is your favorite browser?