Windows remote desktop uses a special protocol that tries to be smarter the just making screenshots and transfer them. To do this it starts the remote session in a special context. Unfortunately this context has limited support for the use of 3D APIs. The exact behavior depends on the operation system version. I cannot remember the exact details but IIRC this context doesn’t provide DirectX 9 devices at all. This might be changed with the last service pack for Windows 7.
I have discovered that web browsers viewed via Windows remote desktop do not support WebGL even if they are told to ignore the graphics blacklist (or force-webgl-enabled in Firefox case). I have tried both Chrome and Firefox 4.
I am surprised. I thought rendering for remote desktop was done on the remote system, the image scaled and the result transmitted to the local system so I expected WebGL to work. The NVIDIA control panel will not open via remote desktop so I cannot check the driver version but I am pretty sure it is WebGL capable.
The information provided at get.webgl.org needs to include this little tidbit.