I have a copy and was running beta 2, but I am not currently testing it right now and its not installed. I wish I could test this for you and find a solution. I found Vista to be a bit too demanding for my system in its current state, and I was reluctant to start using it as my "main OS" especially given the year expirey and thats in beta - I won't have access to more stable builds.

I would say just hold out for now and don't run Firefox. Maybe someone from Mozilla can help you, there are alot of support newsgroups. If someone actually from MSDN comes by maybe they might know whats causing this. I did try to search for a solution for you amid fixing some problems on the website.