however are the cost of developing a web browser and hosting an internet encyclopedia ran by volunteer comparable ?

mozilla use paid labor, engineer who are very expensive. wikipedia it's mostly hosting a html page and a few media.

Yet wikipedia has much more user to whom it can show the donation nag when mozilla has a much more limited userbase.

i think that mozilla taking google money to put them as default search engine is fine, people who care about privacy are allowed to change it whenever they want.