Probably Silverlight, which they have already been using. The thing is, premium content is going to be DRMd whether Firefox users like it or not. The question

Probably Silverlight, which they have already been using. The thing is, premium content is going to be DRMd whether Firefox users like it or not. The question is, will Firefox users be able to consume it once they kill off Silverlight? The only other viable alternative is a native app, and we all know how open and Linux-friendly those tend to be.