Yahoo! is going belly up so not sure they can rely on search agreements for much longer. It's better if they have some direct small individual customers I think.

I'm pretty sure Mozilla has a clause in the contract with Yahoo that covers this: http://www.recode.net/2016/7/7/12116296/marissa-mayer-deal-m...

"According to the change-of-control term, 9.1 in the agreement, Mozilla has the right to leave the partnership if — under its sole discretion and in a certain time period — it did not deem the new partner acceptable. And if it did that, even if it struck another search deal, Yahoo is still obligated to pay out annual revenue guarantees of $375 million."

So if Mozilla goes to another search engine, Yahoo still needs to pay them for nothing? How did Yahoo agree to this?

That's Marissa Mayer for you. [0]

[0] http://www.recode.net/2016/7/7/12116296/marissa-mayer-deal-m...

How would you like Mozilla to be financed?

My point is - I thought they were - by search engine agreements.

That's correct. When you say "self-sustaining", do you mean from direct user donations or paid services (like the built-in VPN example), instead of "selling eyeballs" to Google or Yahoo? There is discussion about creating a Mozilla membership program and what benefits could be offered.