Note, that's Mozilla Foundation which is not the entity that develops Firefox. Money donated via this form would be "used in its discretion for its charitable purposes".

It is somewhat hard to find out what exactly this means, but US form 990 provides an overview (PDF): https://assets.mozilla.net/annualreport/2019/mozilla-2019-fo... , see page 3 and 9

$926K "Agenda Setting" -- published a report

$4,853K "Movement Building" -- urged Facebook, Snapchat, Apple and others to address issues

$10,387K "Leadeship Development" -- Fellowships and awards for technologists and researchers

$1,374K "Compensation of Officers" etc..