Would running their own servers actually be a good idea? Their workloads seem pretty well-served by AWS's offerings: services with extremely bursty traffic (like updates and TaskCluster CI) that can take advantage of the Elastic part of EC2, and mostly-static websites (like MDN and the Firefox installer) that can use a caching CDN like CloudFront.

have you seen AWS/azure/GCP data transfer fees? mozilla would go bankrupt overnight