XP Bros!
*High five*
FF4 looks sexy on XP But how exactly does IE9 integrate W7's features?
IE9 supports jump lists and pinning sites to your tool bar. You can pin a site to a tool bar and it can have specific jump lists for it, aka specific tasks.
IE9 is quality and cranked up the speed quite a bit. I still use FF4 for daily use, but I also have IE9 installed and use it from time to time.
IE9 also supports hardware acceleration for websites (that is to say, loading a website will take greater advantage of the hardware in your computer) and is completely standards compliant with HTML5.