Advertising, tracking, and privacy are three separate concerns. We conflate them due to the way current advertising networks work: they track you, storing + analyzing the data in centralized servers (which violates your privacy), to deliver ads.
You can deliver ads without tracking (for example, contextually based upon the page you are looking at, without any storage of that information or historical state.) And you can track users without violating their privacy (by not sending the data to a remote server and only analyzing it locally.) So in general, it's certainly possible to be able to preserve a user's privacy while also be monetizing your product through advertising.
Now of course, most people dislike ads, which is a separate issue. But advertising is not inherently a violation of privacy, at least if you see privacy through the lens of surveillance by a third party. (You could stretch the definition of privacy to a point where seeing ads I suppose could be privacy violating, but I don't feel my privacy is being violated when I see a billboard on the highway, for example.)
Advertising is an issue of user autonomy and a user's security in their autonomy. Users don't want to see ads. A browser that is supposed to be "for the users" shouldn't have its main screen be something that their users specifically do not want.
For most of us, adware is a type of malware. For Mozilla, they have a tradeoff between user autonomy and cash flow. They can at least say that the bad things they do are because of the sacks of cash and not for any positive user "experience." Lying about it makes it worse, not better.
Aside from ads, there is the issue that Firefox comes with backdoors (see Mr. Robot ad) and spyware (see telemetry that can't be opted out of.)
Which bits of telemetry can't be opted out of? I've set at least a hundred things in my about:config to tamp down on it but I'm never quite sure I've got all of them.
I'm one of those "don't mind ads, do mind privacy intrusions" crowd. I'd be perfectly willing to turn off my adblocker for good if only advertisers would be willing to turn off their tracking and scripts and stick to only serving up JPEG banners.
Alas, that's not likely. So I do what I can to use web services ethically - pay for services where possible (like Fastmail), whitelist when a site owner seems to be using ethical non-tracking ads, donate where appropriate (like open source developers looking for help with hosting fees).
the data can be processed locally, but when my browser says, “get me the ad about debt relief”, it's leaking private info. that's why contextual ads are always better.
You can deliver ads without tracking (for example, contextually based upon the page you are looking at, without any storage of that information or historical state.) And you can track users without violating their privacy (by not sending the data to a remote server and only analyzing it locally.) So in general, it's certainly possible to be able to preserve a user's privacy while also be monetizing your product through advertising.
Now of course, most people dislike ads, which is a separate issue. But advertising is not inherently a violation of privacy, at least if you see privacy through the lens of surveillance by a third party. (You could stretch the definition of privacy to a point where seeing ads I suppose could be privacy violating, but I don't feel my privacy is being violated when I see a billboard on the highway, for example.)