I have several Firefox Add-Ons. One is Flashblock (v1.5.18). This is supposed to replace Flash objects with a button that can be pressed to allow the blocked item. Unfortunately it's not giving me a button to press on that blank screen that should be showing me the initial rotating balls screen. Neither is adding the SkyDemon URL to its whitelist improving things.
I'm sure the gurus at SkyDemon might be able to suggest another item to add to the whitelist, but I can't guess it.
Meanwhile, I've disabled Flashblock and all is restored.
But I'd be happier if I could have my Flashblock back, protecting me from other c**p.
Hope this is useful to others.