I’d be surprised if close to 100% of those users aren’t using Chrome, not Firefox for any streaming purposes.
https://news.ycombinator.com/item?id=44294402
So they use Firefox 99% of the time and then if they encounter the rare thing that requires DRM they treat it like toxic waste that has to run in an isolated sandbox, which doesn't need to be the same browser they use for anything else.
The only other sensible option is to get out the reversing toolkit and break the DRM.