IIRC non-profits can't make and keep profits.
Corps can, hence Mozilla Corp. They can keep profits around in order to.. like, purchase Pocket, or simply pay employees later when Mozilla makes less profit, or whatever else.
These things are hard or maybe impossible in a non-profit (IANAL/correct me if I'm wrong)
Non-profits can make surplus revenues over costs and retain them; they can't return profits to shareholders or other particular beneficiaries.
Certain classes of nonprofits are restricted from certain business activities, or limited to certain activities. E.g., charities (501c3 nonprofits) must be organized and operated exclusively for purposes on an list of charitable purposes.
Yes, nonprofits can charge money and hold onto it. What they can't do is distribute it to shareholders. Many universities are nonprofits, and they hold on to millions or billions of dollars. Nonprofits can also acquire companies, etc.
The terms "nonprofit" and "not-for-profit" are unfortunate misnomers. Like any other company, nonprofits can offer gainful employment and will eventually bankrupt if they never turn a profit.
These things are hard or maybe impossible in a non-profit (IANAL/correct me if I'm wrong)