It implies maintaining the browser would better fund the mission in the long run than selling user data to adtech now as the user count continues to decline.
Google pays Apple 18 billion dollars per year to be the default search engine on Safari. If Firefox had managed to stay just as popular imagine how much more money they'd have been making on search deals these last 5 years and how much of that could have went to whatever mission they wanted. Instead they've got a whole lot of noise adding up to about nothing for income + a much smaller search deal than they should have. That's why "having a social mission" isn't inherently the issue, it's all about the management around balancing how the investment for the social mission is done.
I think GPs numbers are off by an order of magnitude or so though. I remember reading something like Mozilla spending 200 million/year on software development (not all Firefox) so it might take 300+ million/year just on Firefox to really have a big impact from status quo. Someone with the real numbers is invited to correct me on that. Browsers have huge teams of people, even Ladybird is using large components like Skia developed by other browser teams.