Glitches in Firefox when hardware acceleration and WebRender are enabled

System information

System:    Host: arch Kernel: 5.10.37-1-lts x86_64 bits: 64 compiler: gcc v: 11.1.0 Desktop: Xfce 4.16.0 tk: Gtk 3.24.24 
           wm: xfwm4 dm: LightDM Distro: Arch Linux 
CPU:       Info: Dual Core model: Intel Celeron N2840 bits: 64 type: MCP arch: Silvermont rev: 8 cache: L2: 1024 KiB 
           flags: lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 8666 
           Speed: 656 MHz min/max: 500/2582 MHz Core speeds (MHz): 1: 656 2: 917 
Graphics:  Device-1: Intel Atom Processor Z36xxx/Z37xxx Series Graphics & Display driver: i915 v: kernel bus-ID: 00:02.0 
           chip-ID: 8086:0f31 
           Device-2: Chicony HD WebCam type: USB driver: uvcvideo bus-ID: 1-3:2 chip-ID: 04f2:b490 
           Display: x11 server: X.Org 1.20.11 driver: loaded: intel unloaded: modesetting,vesa alternate: fbdev 
           resolution: 1366x768~60Hz s-dpi: 96 
           OpenGL: renderer: Mesa DRI Intel HD Graphics (BYT) v: 4.2 Mesa 21.1.0 compat-v: 3.0 direct render: Yes 

Describe the issue

Glitches appear in Firefox when hardware acceleration is enabled and WebRender compositor is used. This happens when "Use recommended performance settings" and "Use hardware acceleration when available", which are the default settings, are checked.

Same glitches disappear when these options are disabled. This is particularly problematic for me because when these options are disabled, hardware accelerated video decoding is unavailable. I'm using Firefox version 88.0.1 and these glitches appear both on the UI and on the web pages. No issues with Chromium when hardware acceleration is enabled.

A bug report already exists for Firefox but we were suggested to do the same for Mesa. Here is the link :

https://bugzilla.mozilla.org/show_bug.cgi?id=1708682

about.support.with.issue.txt about.support.without.issue.txt dmesg.log xorg.log