I never stand still. I always run away unless I've commited to jumping the fireball.
The code says fireball behavior is random. Some people believe you can influence the fireball behavior. The most common belief is charging the fireball will make it retreat. I think that originated from the Consumer's Guide "How to win at Donkey Kong." While I do believe you can influence the fireball behavior, I think sometimes you influence it to your advantage and other times to your disadvantage. As an analogy, consider a coin flip. 50/50 heads/tails. Now if a wind blows the coin, does it influence the outcome? Yes, but it's still random.