I can't really recall any decisions made that were unpopular with existing users, but likely to lure new users in. Ads on new tabs doesn't seem like something that would bring new users in. Pocket doesn't either, since iirc you could install the extension in Chrome if you really wanted it.
Most of the controversies I remember were either to increase Mozilla's revenue, or boondoggles like their mobile OS. My major annoyance was that the increase in revenue seems like it was spent on boondoggles or weird, unrelated charity rather than going back into improving the browser.
I'm still also a Firefox user, but it's like 99% because ads are not their primary source of revenue rather than any remaining fondness towards Mozilla.
But, also, bringing money in is proxy enough for being able to do "good" for whatever definition we'd like to use. So, money or users, I think my general point about compromising their ideals for pragmatism is still valid (not necessarily true or correct, but it's an argument that can potentially be made).