It's not 'one day', the majority of Mozilla's funding has always come from 'search royalties'. Wikipedia says initial funding first came from AOL in 2003, then they had a deal with Google from 2004-2014. In 2014, it says they signed a deal with Yahoo. This is nothing new.
and yet it was the only browser that really opposed EME, and only backed down once not only every browser had implemented the extension, but many major media providers too. Basically once the browser became useless for media consumption because of it.
https://en.m.wikipedia.org/wiki/Mozilla_Foundation#Financing