I have just installed MSIE 9 and Firefox 4 rc2 on my computer.
User interface on both browsers are similar. Firefox'es home-button moved to right of url bar. Just back-forward buttons are visible. Tabs are on the top. Url-bar are shorter.
Javascript performance on both systems are similar. Some tests with jquery gave Firefox more points. But Firefox still needs more ram than msie.
Both systems support HTML5 and CSS3.
The visual difference between MSIE8 and 9 is more than the one between Firefox3 and 4.
Firefox let resize textareas.
