[Affected versions]:
Nightly 80.0a1 (2020-07-14)

[Affected platforms]:
Platforms: Mac Os

[Preconditions]
Have gfx.webrender.all - true

Steps :

1. Launch the Firefox browser and reach about:preferences
2. Scroll the page up and down

Expected Results :
No visual glitches should be displayed.

Actual Results :
Black glitches are displayed with WebRender on.

Please note that this issue only started to occur in todays build. The build from 07/14/2020 is not affected by this issue.

Rares, can you attach the about:support for the machine you were using when you saw this? I am on 10.15.5, Intel 655 - can't yet seem to reproduce this.

Maybe this is a dupe of: https://bugzilla.mozilla.org/show_bug.cgi?id=1652763 - in which case, the offending issue was backed out. So this might not happen now.

I have attached the about support file from the macbook I tested on

Hi,

I'm not able to reproduce in macOs 10.12.6 (16G2136), GPU Radeon Pro 555 2048 MB.

Best,
Clara

Can you update to the latest Nightly and see if this still happens?

I retested this in our latest nightly build 80.0a1 (2020-07-16) and it no longer occurs, I think we can close this issue as well as the other one with Pinterest.

This issue is verified as fixed in our latest nightly build 80.0a1 (2020-07-20) on Mac OS 10.14.6

Bug 1653413 fixed DirectComposition for Win10.
As this occurred on macOS and seems to be fixed, the backout of bug 1640960 might have fixed it:
Your build 20200714083249 is the first that contained bug 1640960 comment 3. Its backout (bug 1640960 comment 6) was merged one build later (20200714214702).
Then it was merged again in bug 1640960 comment 11 (20200715215205) and backed out again in bug 1640960 comment 14 (20200716212737).