On the linked report above I'm seeing software development as about 52% of their expenses. And many of the other expenses, eg "General and administrative", I understand to be support infrastructure for software development. This would seem to fit the meaning of "most" on my read.

It's really telling that Mozilla does not want to itemize those costs to say how little the actually use on Firefox.

Saying "Mozilla doesn’t itemize expenses" is like saying a university's annual financial report is hiding cafeteria costs because it doesn’t list fruit cups separately.

Large nonprofits publish consolidated, high-level statements that group expenses by broad function, not by department or line item because that's the correct level of financial reporting for external audiences.

If they misrepresented their spending that would be flagged by the independent auditor. It's deeply responsible to accuse them of hiding something when you have no baseline concept of standard disclosures.

They're not hiding anything they're legally required to disclose, but that's a very low bar.