I had the same problem using both miro 4 and 5 however i found a fix and believe it will be added to version 6
gksu gedit /usr/share/pyshared/miro/plat/frontends/widgets/application.py
find
gtk.gdk.threads_init()
replace with
gobject.threads_init()
save close
then
gksu gedit /usr/share/pyshared/miro/plat/frontends/widgets/webkitbrowser.py
find and remove the 4 lines below plus the extra blank line under settings.set_property('enable-plugins', False)
#this disables all plugins -- Miro has problems with the
# adobe flash plugin and hangs when the plugin loads and starts
#this disables all plugins -- Miro has problems with the
settings.set_property('enable-plugins', False)
remove/save/start miro and now hulu and other flash sites should work through the miro browser