Just adding that as I understand this, donations to the Mozilla Foundation cannot go towards Firefox, because it's [edit: Firefox is] actually part of the Mozilla Corporation. To help with funding Firefox people can consider purchasing the Corporation's other products (VPN/Relay/Monitor), or purchasing merch.
See more here on the AMA on Reddit, and this thread
for anybody that wants to disable it, go to the settings and search for "Allow websites to perform privacy-preserving ad measurement"
(or through the
dom.private-attribution.submission.enabled
flag inabout:config
)https://support.mozilla.org/en-US/kb/privacy-preserving-attribution