Could be one of those C-suite power plays:

Texeira is managing their one profitable product profitably and looks destined to be CEO.

The old CEO Baker suddenly resigns, and appoints Chambers as (permanent) successor CEO.

Chambers and/or Baker is in tight with the head of HR Chehak, and gets her to declare that Texeira is physically unfit for his job as Chief Product Officer or any other job at Mozilla.

Chambers and/or Baker get their wish for Chambers to become CEO;

Demonstrably competent exec Texeira is essentially out of a job;

Great success!