Yup Xenforo definitely looks better in firefox but for me IE8 render xenforo pages way faster than firefox, the difference between IE8 and firefox 3.6.14 is alot more noticeable in xenforo forums than vB forums or on wordpress sites!
I do a lot of cut and pasting of visitor data from the who's online list on vB as part of management, IE has always worked better for that task, in fact perfectly versus other browsers like Firefox or Opera.
I hate IE as a browser, last version I used a lot which I did enjoy using was IE6. After that it all went downhill fast! I only ever use IE8 (updated from 6) for testing site viewing changes only with it, same with Chrome as well. Just so I can check if the forum is cross-browser compatible with those 3 major browser used by people.
It's only a Tech Community Preview, it doesn't even have any browser chrome, it's just literally a rendering engine so that web developers can see how it works and plan ahead. IE10 itself won't release for another 18 or so months, and I wouldn't think that we will even see beta's for another 10 or so months, let alone any RCs.