Earlier quoted context omitted.
Chromium is technically free software, yes, but it's a horrible example of it. Because Google entirely controls code contributions to it. Only a fork could be amended the way that the community wants it. The same is obviously true for Firefox, with Mozilla being the gatekeeper, but this is where non-profit vs. for-profit does come back into play. As for bad things in Chromium, as well as a fork that tries to fix it:…
So you say that the basic difference is the non-profit status of Mozilla, in a discusion about things that Mozilla does to make money. I'm not convinced. Non-profit status doesn't mean that they refuse to take money, but that there are no stock holders. The organization as such is still interested in maximizing revenues and people working in it are not necessarily volunteers. How is decided who works for Mozilla and…
So, there's actual clear specifications of what they're allowed to do and what not. I don't know the exact ramifications either, but some important points are that they're not allowed to keep more than a set amount of money and that any money they get a hold of, which exceeds this amount of money, they have to invest into their specified mission (which in the case of Mozilla is to make the internet a healthier place: https://www.mozilla.org/en-US/mission/).
They are allowed to pay people appropriate wages, but as you've already pointed out, there's no stock holders. No one gets paid out extra money when they make extra profit. They are legally bound to reinvest this money into their mission.
And there's also the Mozilla Corporation. The Corporation is not legally a non-profit. So, they don't get tax exemptions, but can keep around as much money as they want. So, in a way, they can make a profit, which is by increasing the amount of money they keep in their bank account.
However, they are a 100% subsidiary of the non-profit Mozilla Foundation. So, the Mozilla Foundation is their only stock holder. If they do make extra profit, they either have to reinvest it right away, put it on their bank account to reinvest later, or they can pay it out to the Mozilla Foundation, where it's again in non-profit hands, and is therefore legally enforced to be reinvested into Mozilla's stated mission. In other words, it's not possible for the Corporation to make profit which is not at some point reinvested.
The Corporation being a subsidiary also means that the Mozilla Foundation holds sovereignty over the Corporation. They can throw out Mitchell Baker (Executive Chairwoman) or Chris Beard (CEO) and set their wages.
So, the Corporation has motivation to make a profit, because the Foundation could throw out their key people, which in turn could throw out any slackers within the Corporation.
The Foundation also continues to hold the Firefox and Mozilla trademarks and has the final say of what's included into Firefox's source code.