To me, the governing text on the Fog of War card is the last sentence: "Cancel the card." Thus, when a Uranus card is played for its text effect (as opposed to its Firefight value), and a FoW card is played in reply, the Uranus card is cancelled and immediately discarded. This is supported by the second example given in the Canceling an Action section on rulebook page 5.
Thanks for your feedback, Jim. I still don't think the situation is clear. When is the Uranus card text effect "played"? When the card is brought into play, or at the instant the effect is to occur? I think the former is very questionable. The example you cite doesn't clarify the issue because it doesn't address this central question.
One-time actions are clearly canceled by Fog of War resulting in discard of the card. Uranus cards can be described to be recurring actions. Discard of a Uranus card normally requires the Germans implement the red text at the bottom of the card.
I'd like to hear other's perspective. Even if what I'm talking about is not the designer's intent one could use my approach for play balance if some think the Germans have a meaningful advantage.