A CEO should be paid enough to live comfortably if you work at a non-profit, but if you need to be paid market rate then you're probably not passionate about the position. When your job is fulfilling a public good rather than delivering shareholder value, that and a decently generous salary should be reward enough.

That said, I think Signal is better than Mozilla on this front, because they don't have a long history of terrible decisions each of which coming with increased executive compensation.

EDIT: Also the CEO of Mozilla made 6-7 million per year (haven't checked the new CEO though). Way more than Meredith Whittaker's $750,000. So honestly Signal is an order of magnitude better on this front.