[Tloewald]

I agree, but of the four major browsers, two are directly underwritten by advertising (Chrome and Mozilla) and Microsoft is moving that way.

Only Apple has backed off advertising as a revenue source, so it basically comes down to Apple being willing to cause massive breakage (the way it did with Flash) in pursuit of a principle. The fact that they enabled ad blockers in mobile safari says they are at least sympathetic to the idea.

[rodorgas]

Did you mean Mozilla is an ad driven company?

[kijin]

A very large percentage of Mozilla's revenue comes from search engines (recently Yahoo, previously Google) who pay Mozilla to make themselves the default search engine on Firefox. If Firefox users saw no ads and were untrackable, Yahoo would have no reason to pay anymore.

Of course Mozilla doesn't try to force everyone to stick to the defaults, so you're free to change the default search engine and install a bunch of ad-blocking, anti-tracking add-ons.