Try open the race in a new tab instead of a new window.
Sounds silly I know!
But opening the race in a new window the computer thinks you have 2 web browsers open.
Where as opening the race in a new Tab, it only lists one browser in use on the computer in the task manager.
DirectX End-User Runtime Web Installer https://www.microsoft.com/en-gb/download/confirmation.aspx?id=35
It will give you the D3D9 API if you cant use D3D11
In about:config Make sure media.hardware-video-decoding.failed = false
I had the same trouble during the beta,only thing i could get working was the developer version of chrome. I cannot access my desktop at the moment, I have a laptop and an ipad, neither of which can I get the viewer to work
Fortunately my Work PC has saved the day (after my home PC and my Work Laptop failed to open it up). That, however, is a pain for races when i am not actually in the office...!