>For almost any non-profit maintaining their new donations for the same level for 5 years would be considered good performance

Donations are barely a factor here, it is not a meaningful part of their revenue.

As you say, one year of steady revenue would cause a significant shakeup in a company. By year three, things would look fairly dire. Mozilla has already tried a number of other options, and are in the middle of a management change. Eventually this becomes the only choice