With Firefox's default search engine back to Google, I find last year's piece very relevant. [recode.net]
Basically, Verizon (the eventual new Yahoo owners) has to pay Mozilla $375 million annually through 2019 due to the breakup clause due to Mozilla backing away because it's not satisfied with Verizon and I can't blame them. Firefox 57, which launched today, They changed their default to Google again which it all makes sense now.