According to Wikipedia[1], most of Mozilla is funded by Google, for setting them as the default search engine, rather than by more conventional advertisers.
On a more personal note, I'd prefer if that money went towards improving their FOSS offering instead of giving the now-former CEO a $7M bonus[2], acquiring advertising businesses [3][4], and littering Firefox with these anti-features.
[1]: https://en.wikipedia.org/wiki/Mozilla_Corporation#Google
[2]: https://en.wikipedia.org/wiki/Mitchell_Baker
[3]: https://blog.mozilla.org/en/mozilla/mozilla-anonym-raising-t...