ViewAbout 2.0 seems to be broken on Firefox 4 Beta 1. The about: windows now only show up as grey panes.
I suspect they might be due to the following changes, but I don’t know for sure and might not have much time with the impending school semester ahead of me.
Patches are welcome at Google Code though. 
13xforever | 23-Jul-10 at 3:00 pm | Permalink
They now have about:about built-in, so I think this addon is not needed anymore.