You may be right, but I'm not sure we actually have strong evidence for that. Mozilla has run like a bigtech firm for so long that it's not really clear whether the open-source portion thereof could survive without.
$500 million in annual revenue and $6 million CEO compensation packages are well in excess of what other similar-scope projects get by on. Mozilla accounts for somewhere between 30-50% of all funding in open-source - if you sum up the Linux foundation, the Wikimedia foundation, the Apache foundation, KDE e.V, the Gnome foundation... it's still less than Mozilla