User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:82.0) Gecko/20100101 Firefox/82.0

Steps to reproduce:

Enabled MOZ_X11_EGL=1, gfx.webrender.all=1, and updated Nightly to 20200904094341

Actual results:

Compositing fallback to Basic on EGL.

Failure Log
(#0) Error Failed to create EGLConfig for WebRender with depth!
(#1) Error Failed to create EGLConfig for WebRender with depth!
(#2) Error Failed GL context creation for WebRender: 0
(#3) Error Failed to connect WebRenderBridgeChild.
(#4) Error Failed to create EGLConfig for WebRender with depth!
(#5) Error Failed to create EGLConfig for WebRender with depth!
(#6) Error [OPENGL] Failed to init compositor with reason: FEATURE_FAILURE_OPENGL_CREATE_CONTEXT

Expected results:

WebRender should running on EGL as normal.

Please open about:support, click on "Copy text to clipboard" and paste it here. Thanks!

Here is the about:support data.

I can reproduce this with KDE X11, Debian Testing.
$ MOZ_X11_EGL=1 mozregression --launch 20200904094341 --pref gfx.webrender.all:true -a about:support

MOZ_X11_EGL=1 mozregression --good 2020-09-02 --bad 20200904094341 --pref gfx.webrender.all:true -a about:support

3:29.60 INFO: Last good revision: aa032cbc94551a0f6e7e821d78aa0388f998e830
3:29.60 INFO: First bad revision: bb0078598fc8d05033d58cd7c8963ec14a5b3925
3:29.60 INFO: Pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=aa032cbc94551a0f6e7e821d78aa0388f998e830&tochange=bb0078598fc8d05033d58cd7c8963ec14a5b3925

bb0078598fc8d05033d58cd7c8963ec14a5b3925 stransky — Bug 1460959 [Linux] Implement nsWindow::IsMainWindowTransparent(), r=jhorak
2f0cdb92820d81021fe9ec55318f09c1a98bdaa4 stransky — Bug 1460959 [Linux] Disable titlebar by default when we can paint the titlebar transparent corners, r=jhorak
c22047618d6dc818f77f75d8f5ef743f8063b68b stransky — Bug 1460959 [Linux] Use alpha visual for Firefox toplevel window on composited screens, r=jhorak
9b0831b5b79dd1a355ed3988e58910aec79b7b61 stransky — Bug 1460959 [Linux] Clear alpha channel from decoded video on BasicCompositor, r=sotaro

Only EGL is affected, GLX is unaffected.

Can confirm it does not occur in other DEs. Started in kde after 5th September update. Last update was 3rd September

Okay, I'll look at it.

Seems to be solved somehow. about:support is showing webrender. The only problem seems to be a black outline surrounding every element, such as menu, downloads, library etc

Video to demonstrate the black outline

Black border is tracked here at Bug 1663003.

The failed context seems to be already fixed by Bug 1663279.

With 20200909093957 I still don't have title bar and window borders on Debian stable with KDE. Clearing startup cache didn't help, Compositing: WebRender. [EDIT: Wrong bug, sorry]