This has been happening for me for some time now.
I have the 64bit RC, and keep it updated through win updater.
When I want to upload a picture to a website, I click on the "Browse computer" button, when I do the window opens for me to navigate to the picture ... as normal, however all it does is freeze, and then goes into (not responding) mode ?
I have tried it with Firefox and IE, both do the same so its not that, and I have done it on numerous sites, so its not the site?
Can anyone advise here at all ?