"whoever acquires Yahoo might have to pay Mozilla annual payments of $375 million through 2019 if it does not think the buyer is one it wants to work with"

RC:

Mozilla switched to Yahoo from Google after Mayer offered a much more lucrative deal that included what potential buyers of Yahoo say is an unprecedented term to protect Mozilla in a change-of-control scenario.

It was a scenario that Mayer never thought would happen, which is why she apparently pushed through the possibly problematic deal point.