That is true, however routing funds (donations) from foundation to corp is hard, thus only very little $, ¥, €, ... of the money donated go to browser development, while the brand is tightly tied to it. Browser development is funded out of corp budget, which mostly is Google's money for being default search engine. Thus I can't even donate to browser development ...
Now we could speculate how much money they could collect with some Wikipedia-Luke banners in the browser and with the purpose of developing Firefox ... true, less than what Google pays, but how much do they need if they focus on browser (and maybe mail) instead of side projects?
Wikipedia is one of the most-used websites on the planet and they raise ~$90 million a year. That's still only like ~20% of what Mozilla brings in, and I find it unlikely that Mozilla could ever raise that much without driving away users with the annoying ads. That's not a problem for wikipedia because there's hardly a replacement for wikipedia, but there's tons of replacement browsers.
