Nice Firefox Review
Scot Finnie has a very nice review of Firefox, so if you're still on the fence about whether to switch, give it a read. You'll come away with a good feel for what Firefox is all about compared to IE. Most of his "cons" are easily addressed using various Firefox extensions. My favorite that he doesn't mention is called Tabbrowser Extensions, and isn't listed in the normal extension list on the Mozilla site (which is probably why he doesn't know about it). It addresses pretty much every quibble he has with tabbed browsing.
As for RSS handling, skip Live Bookmarks and go straight to Sage. It makes so much sense to keep RSS support in the browser since you're going to be looking at web pages anyway. Sage has the added bonus of keeping feeds in the sidebar, out of the way but easily accessible.
A final extension you need to install is Download Manager Tweak. It adds functionality to the minimalist download manager window.