From selling its "default search engine" spot -- I'm on this web business professionally since 1995, I know that.

That's not direct ad sales and Mozilla wasn't created with the specific purposes to sell ads or collect private information, nor is owned by an ad-selling company.

Besides you can change the default search engine in a heartbeat.

I certainly consider that funding by direct ad sales. It's like any other affiliate model: your contribution is to get their product to be sold.