User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:86.0) Gecko/20100101 Firefox/86.0

Steps to reproduce:

Start Firefox Nightly 86.0a1 with

MOZ_X11_EGL=1 MOZ_LOG="PlatformDecoderModule:5" nightly

and start BigBlueButton WebRTC video conference.

Actual results:

The logs show:

[Child 21838: MediaPDecoder #1]: D/PlatformDecoderModule Sandbox RDD decoder supports requested type
[RDD 22020: Main Thread]: D/PlatformDecoderModule VA-API FFmpeg is disabled by platform
[RDD 22020: Main Thread]: D/PlatformDecoderModule VA-API FFmpeg is disabled by platform
Sandbox: seccomp sandbox violation: pid 22020, tid 22020, syscall 239, args 140720692211076 140707784443464 33 0 0 1.  Killing process.
[Child 21838: MediaPDecoder #1]: D/PlatformDecoderModule Initialising VA-API FFmpeg decoder
libva info: VA-API version 1.10.0
libva info: Trying to open /usr/lib/x86_64-linux-gnu/dri/iHD_drv_video.so
libva info: Found init function __vaDriverInit_1_10
libva info: va_openDriver() returns 0
[AVHWDeviceContext @ 0x7fd9a60e0380] Format 0x41524742 -> bgra.

Expected results:

The message

D/PlatformDecoderModule VA-API FFmpeg is disabled by platform

should not appear as MOZ_X11_EGL=1 is passed, and the configuration options are set correctly.

Or the message should give more details, what configuration option prevents disables the support.

The confusion is, that later on VA-API seems to be used just fine.

I reported the seccomp sandbox violation in https://bugzilla.mozilla.org/show_bug.cgi?id=1683854.

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.