Hi, I just updated to Firefox 119.0 (stable branch), but it flickers momentarily at launch.
The icons for the Firefox extensions in the Firefox toolbar also flicker momentarily at launch.
How can I stop the flickering ?
Please let me know if you need further information to diagnose, thanks.
Terminal errors / warnings at launch :
$ firefox
[GFX1-]: vaapitest: ERROR
[GFX1-]: vaapitest: VA-API test failed: failed to initialise VAAPI connection.
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
I get no warnings - using the same package
firefox 119.0-1 [Installed] extra
Standalone web browser from mozilla.org
What did you change previously with relation to mesa?
ATTENTION: default value of option mesa_glthread overridden by environment.
As far as I know, I haven’t changed any options for mesa.
Well - firefox tells you the value of mesa_glthread is changed compared to the default.
Try opening firefox in safe mode
firefox --safe-mode
Then try a new profile
firefox --ProfileManager
Check the page about:config and search for mesa_glthread
If I open in safe mode, the first two error lines appear initially, but not the last two.
If I try to create a new profile, all four error / warning lines appear.
I don’t see an option for mesa_glthread in about: config – the search result is empty.
I’m running two displays with non-standard native resolutions (each 2560x1440), so not sure if that has something to do with it… just strange as I didn’t have any problems previously.
I don’t have it - anywhere - so one can only speculate.
environment can also reference a value exported to the system somewhere.
One way of determining where is to search folders where such value may be defined e.g.
grep -rl 'mesa_glthread' $HOME/.mozilla $HOME/.config
You will get hits from your .mozilla folder - those wil likely reference this forum thread - but could also indicate where the property is set.
Perhaps the output from below command will provide a clue 
as I have no means of replicating
inxi -CGmxxx
I use Firefox as defacto standard when testing the company’s webapp - (verifiy against IOS Safari, Edge, Vivaldi and Andriod Google Chrome)
I run both Firefox 119.0 and Firefox Developer Edition 120.0
Ok, I get the following output when running these two commands :
(Username in first set of output replaced with XXXXXX)
$ grep -rl 'mesa_glthread' $HOME/.mozilla $HOME/.config
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/29/{26c8480c-3807-4b10-a883-604a547c791d}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/148/{d732d9fa-9b79-45fa-a7bb-9e39c39bf294}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/245/{aa5afbb8-9b17-4098-956c-1613ddf974f5}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/155/{4594a924-2410-4014-a549-d32bb40e4d9b}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/66/{0574e558-442b-473b-b138-79827c001042}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/231/{fc227f7a-165a-4149-9d25-a289c0e2efe7}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/13/{919f4e54-629b-4f48-9199-27f0e35ca20d}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/134/{8241af4e-16d3-4d13-9ff7-6eaf22734e86}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/141/{6bd42dd6-f45c-44c0-9e56-5695d0b0228d}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/135/{4263fc5e-3863-48ff-a22c-dfd52b257387}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/202/{727db988-d57d-4c1d-845a-e01bb371a5ca}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/72/{dad0375a-647e-4fc3-a6be-348c497f3648}.final
/home/XXXXXX/.mozilla/firefox/xc1drikv.default-release/storage/default/https+++forum.manjaro.org/cache/morgue/200/{b4c6b486-e0a7-4c3e-b61a-f0e29789f1c8}.final
/home/XXXXXX/.mozilla/firefox/bzphtjzo.default/storage/default/https+++forum.manjaro.org/cache/morgue/232/{4e80fa0c-c9e3-425e-992a-99e7ee1548e8}.final
$ inxi -CGmxxx
Memory:
System RAM: total: 16 GiB note: est. available: 15.39 GiB
used: 2.86 GiB (18.6%)
RAM Report: permissions: Unable to run dmidecode. Root privileges
required.
CPU:
Info: dual core model: Intel Core i3-7100T bits: 64 type: MT MCP
smt: enabled arch: Kaby Lake rev: 9 cache: L1: 128 KiB L2: 512 KiB L3: 3 MiB
Speed (MHz): avg: 800 min/max: 800/3400 cores: 1: 800 2: 800 3: 800 4: 800
bogomips: 27208
Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx
Graphics:
Device-1: Intel HD Graphics 630 vendor: Lenovo driver: i915 v: kernel
arch: Gen-9.5 ports: active: DP-1,DP-2 empty: DP-3, HDMI-A-1, HDMI-A-2,
HDMI-A-3 bus-ID: 00:02.0 chip-ID: 8086:5912 class-ID: 0300
Display: wayland server: X.org v: 1.21.1.8 with: Xwayland v: 23.2.1
compositor: gnome-shell v: 44.5 driver: gpu: i915 display-ID: 0
Monitor-1: DP-1 model: Lenovo P24q-10 serial: U4P00001 res: 2560x1440
dpi: 123 size: 527x296mm (20.75x11.65") diag: 604mm (23.8") modes:
max: 2560x1440 min: 720x400
Monitor-2: DP-2 model: Lenovo P24q-10 serial: U4P00001 res: 2560x1440
dpi: 123 size: 527x296mm (20.75x11.65") diag: 604mm (23.8") modes:
max: 2560x1440 min: 720x400
API: EGL v: 1.5 hw: drv: intel iris platforms: device: 0 drv: iris
device: 1 drv: swrast surfaceless: drv: iris wayland: drv: iris x11:
drv: iris inactive: gbm
API: OpenGL v: 4.6 compat-v: 4.5 vendor: intel mesa v: 23.1.9-manjaro1.1
glx-v: 1.4 direct-render: yes renderer: Mesa Intel HD Graphics 630 (KBL GT2)
device-ID: 8086:5912 display-ID: :0.0
I have a laptop with Intel HD Graphics 620 installed with Manjaro Plasma and the same message is displayed when starting from konsole - no flicker though.
It is likely because Firefox detects the i915 driver and because of the environment the glthread message is displayed - and it is excatly that - an informational message.