Marketing is not just ads. They support a lot of projects like the Stupid Shit No One Needs & Terrible Ideas Hackathon[1], the Gigabit Community Fund[2], the Hive NYC Learning Network[3], and many more, which probably are itemized as marketing.

[1] http://stupidhackathon.github.io/

[2] https://www.mozilla.org/en-US/gigabit/

[3] http://hivenyc.org/