People would like to donate directly to Firefox, but as things stand, this isn't an option. This isn't because Firefox falls under the Mozilla brand, it's because Mozilla choose not to accept Firefox-specific donations.
https://news.ycombinator.com/item?id=24141852
https://assets.mozilla.net/annualreport/2018/mozilla-2018-fo...
edit: More broadly, pointing out someone as making a false statement does not mean you agree with the opposite view, simply that you don't like people spreading false statements.
A related point on fungibility turned up in earlier discussions: donating directly to Firefox might not count for much if Mozilla balance it out by redirecting the same sum of their general fund away from Firefox. [0][1]
Overpaid relative to what? Other CEOs of similar sized non-profits? Do you have evidence to support that claim?