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In Firefox with WebRender enabled text becomes garbled at the bottom of long pages, with r600 driver:

It is expected that text is clearly visible, like if running with llvmpipe:

Related issue

This issue in Mozilla bug tracker https://bugzilla.mozilla.org/show_bug.cgi?id=1673939

API Trace

firefox-long-page.trace.xz

Steps to reproduce

1. Start firefox browser
2. Make sure webrender is enabled: go to about:config, accept warning and set gfx.webrender.all value to true
3. Exit and start firefox browser again
4. Open long text page https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.8.15
5. Go to end of page, try reading text.

Repro Rate

5/5

Environment

Mesa

• 20.2.1
• recent GIT master build

Firefox

• from Firefox 69
• up to current 82.0.2
• Firefox Nightly 84.0a1 20201030034830

System information

System:    Host: skyserv Kernel: 5.9.2 x86_64 bits: 64 compiler: N/A Desktop: KDE Plasma 5.20.2 tk: Qt 5.15.1 wm: kwin_wayland
           dm: SDDM Distro: Gentoo Base System release 2.7
CPU:       Info: 6-Core model: AMD Phenom II X6 1055T bits: 64 type: MCP arch: K10 L2 cache: 3072 KiB
           flags: lm nx pae sse sse2 sse3 sse4a svm bogomips: 33601
           Speed: 800 MHz min/max: 800/2800 MHz Core speeds (MHz): 1: 800 2: 800 3: 800 4: 800 5: 800 6: 1486
Graphics:  Device-1: Advanced Micro Devices [AMD/ATI] RS880 [Radeon HD 4290] vendor: Micro-Star MSI driver: radeon v: kernel
           bus ID: 01:05.0 chip ID: 1002:9714
           Display: wayland server: X.Org 1.20.8 compositor: kwin_wayland driver: radeon FAILED: ati
           resolution: 1920x1080~60Hz s-dpi: 96
           OpenGL: renderer: AMD RS880 (DRM 2.50.0 / 5.9.2 LLVM 10.0.1) v: 3.3 Mesa 20.2.1 compat-v: 3.0 direct render: Yes