On my blog on StefaniPartin.com, I have had this problem for as long as I can remember. When I go to create a link from the visual editor, the box will popup and nothing will show. I can't even close this box. I end up having to close the whole Firefox window. So normally, I have to create the link in the code section.
Today, I decided to see if i could get rid of this problem by adding the WYSI editor plugin. I activated it and the same thing happens. Any time I try to click on an option that opens a popup, it will open but its blank.
I found a link online with someone with the same problem, but no real solution listed there:
http://en.forums.wordpress.com/topic.php?id=14578&page
Any ideas?