User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0

Steps to reproduce:

Hi,

My hardware is made of :

• LCD TFT Hewlett Packard 22" 16:9 1920x1080
• CPU Intel Core 2 Duo E7200 @ 2.53GHz "Wolfdale"
• Motherboard ASRock Conroe 1333 DVI/H R2.02 with Intel GMA 950 "Gen3"

Here are the details :

$ uname -a
Linux ab-ex73jqs3f7ht 4.9.0-9-amd64 #1 SMP Debian 4.9.168-1+deb9u2 (2019-05-13) x86_64 GNU/Linux

$ lspci -nnk | grep -i vga -A2
00:02.0 VGA compatible controller [0300]: Intel Corporation 82945G/GZ Integrated Graphics Controller [8086:2772] (rev 02)
Subsystem: ASRock Incorporation 82945G/GZ Integrated Graphics Controller [1849:2772]
Kernel driver in use: i915

$ lspci -v
00:02.0 VGA compatible controller: Intel Corporation 82945G/GZ Integrated Graphics Controller (rev 02) (prog-if 00 [VGA controller])
Subsystem: ASRock Incorporation 82945G/GZ Integrated Graphics Controller
Flags: bus master, fast devsel, latency 0, IRQ 16
Memory at fe980000 (32-bit, non-prefetchable) [size=512K]
I/O ports at dc00 [size=8]
Memory at d0000000 (32-bit, prefetchable) [size=256M]
Memory at fe940000 (32-bit, non-prefetchable) [size=256K]
[virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
Capabilities: <access denied>
Kernel driver in use: i915
Kernel modules: i915

Actual results:

1°) There is important tearing while scrolling with Firefox 66.0.5 and compositing = basic (from about:support page) on Debian GNU/Linux 64 bits Stable (see capture attached) .

2°) Tearing totally disappear once WebRender is activated (= after having switched gfx.webrender.all to true and restarted Firefox. Then about:support page says : compositing = Open GL)
And scrolling is at least as smooth as before (maybe smoother, not sure)

Expected results:

I suggest to activate WebRender to suppress tearing

Is this a regression?

https://en.wikipedia.org/wiki/Intel_GMA#GMA_950

GMA 950 supports [...] OpenGL 1.4 [...]

WebRender requires OpenGL 3.2 / OpenGL ES 3.0. Firefox falls back to "OpenGL" compositing since gfx.webrender.all implies layers.acceleration.force-enabled.
You could try starting Firefox with environment variable LIBGL_ALWAYS_SOFTWARE=1 (software rendering on your CPU). "Compositing" should be "WebRender" then. How does it perform?

(Is tearing with Basic a regression or has it happened with previous Firefox versions as well?)

I'm not sure if it's a regression (that's my father's PC that I only maintain) but I've noticed that switching to OGL compositing solved the important tearing problem that I've noticed at that moment while scrolling about:support page (tip : scrolling pages like about: support is helpfull to detect tearing since it displays a lot of horizontal lines!).
I'll try with Firefox ESR to compare since it's also installed on his system.

Plus I'll try Jan Andre Ikenmeyer suggestion and will let you know

Thanks

Hi again,

1°) Firefox ESR with "basic" compositing also suffers from major tearing while scrolling.
Even with addons deactivated (Safe mode).
Swithing to "OpenGL" compositing by turning gfx.webrender.all on solve the tearing problem like with Firefox 66.

2°) Not sure how to set environment variable LIBGL_ALWAYS_SOFTWARE=1
In a terminal, I've keyed
$ export LIBGL_ALWAYS_SOFTWARE=1
then
$ printenv LIBGL_ALWAYS_SOFTWARE
1
Is it ok ?
Then I've started Firefox 66 with gfx.webrender.all switched to true
about:support still says compositing = Open GL
Still no tearing but this page is blurry! See screenshot attached

Thanks

Bugzilla seems to be the lonely site to be blurry, that's strange

Hello, I've noticed that even the purple shield icon in url bar is blurry while the page is loading !

How can I unset software rendering ?

Thanks

Close the terminal, set LIBGL_ALWAYS_SOFTWARE to 0 or reboot your computer. Such an environment variable is only valid for a session.

Ok thanks
But I have that blurry thing with Compositing = OpenGL, no matter how many time I reboot
Switching back to Compositing = basic remove the blur (but bring back tearing).

About tearing, maybe the related bug is https://bugzilla.mozilla.org/show_bug.cgi?id=1127910

And that bug also notice that tearing disappear with OGL compositing https://bugzilla.mozilla.org/show_bug.cgi?id=1274686#c0

Also, about tearing on GNU/Linux with software compositing https://bugzilla.mozilla.org/show_bug.cgi?id=1420712#c4

GMA 950 supports [...] OpenGL 1.4 [...]

WebRender requires OpenGL 3.2 / OpenGL ES 3.0.

• Tearing with "Basic" would be a duplicate of bug 1420712.
• Blurry "OpenGL" would be moved to the Graphics component and probably not receiving much attention, as "WebRender" is being rolled out to Linux. ("OpenGL" compositing is layers.acceleration.force-enabled;true without enabling any WebRender pref.)
• You could try out software rendering with WebRender when it's ready to test. It's on the roadmap and would be prepared in bug 1548395.

Ok, thanks

Thank you for investigation!
I'm going to mark this as duplicate, as advised.