The advanced configuration string is a critical, lower-level browser preference primarily found within the Mozilla Firefox and Waterfox about:config architecture. It commands the web browser to use the Direct3D 11 backend via the Windows Media Foundation (WMF) framework to execute DirectX Video Acceleration (DXVA) . When enabled, this flag shifts the heavy burden of high-definition web video playback from your CPU directly to your dedicated or integrated Graphics Processing Unit (GPU).
If you are experiencing video rendering anomalies, you can test or adjust this setting directly via the Firefox configuration panel: mediawmfdxvad3d11enabled