Firefox gets its revenue from ads. Whether directly or indirectly, through first Google, then Yahoo, and now directly. They never seem to have enough revenue.
Wikipedia gets its revenue from donations. They occasionally have a beg bar at the top. They refuse to accept advertising. They always seem to have too much revenue.
I, for one, would much prefer to have an occasional beg bar in my Firefox and no ads, rather than ads and no beg bar.