Google didn't donate money to Mozilla (not large-scale anyway), it paid for being the default search engine just like it pays Apple and Opera, for instance. Very traditional business deal.
Well, it is traditional now, but it wasn't at the time.
I'm not quite sure what you mean. It was a revenue sharing deal at that time and very orthodox at that. It was new in that it was the first time a search / advertising company paid a browser vendor, but that doesn't make it a one-sided charity act or some special kind of deal that could be summarized appropriately with "Google funding Mozilla", as this only tells half of the story.