I'd never go back to IE.
There are some sites that are so anal - you need IE to get them to render correctly - they insist on using a lot of FrontPage specific coding that does not adhere to the current W3C conventions. So for that reason and only that reason I keep IE around.
There are a few add-ons I really like,
ReminderFox - lets you set up events/tasks/appointment/etc from within Firefox
NoScript - blocks all sorts of nasties - and allows you control over which sites load various types of scripting
Print/Print Preview - replaces the standard Firefox Print button to allow you to preview the page before wasting paper on printing a page with just a line or two of unneeded stuff
There are hundreds of add-ons on the
Mozilla site - have fun searching.
Just click on the
bolded text above to go and look.