2027221 - WebRender Compositor is Bugged in Firefox 149

Status: RESOLVED WORKSFORME

(Core :: Graphics: WebRender, defect, P1)

Description

[[e-mail]]

Steps to reproduce:

Updating to Version 149.

• Have gfx.webrender.layer-compositor set to true
• Play a youtube video / live stream and minimize the window
• After a while restore window, the window flashes black trying to restore contents, sometimes it can't restore contents
• If you have other windows open, they will flash and stay blacked out until you click to bring them to foreground.

Actual results:

Firefox windows flashes black instead of restoring the content. It also tends to break playback of content, forcing some content using AV1 into VP9 for some reason, even if your hardware is able to decode it.

Expected results:

Restore windows as usual, like version 148.0.2

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Graphics: WebRender' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Alice0775 White]

I can reproduce the issue on Nightly151.0a1 Windows11.
Screencast: https://youtu.be/VybSf-VBbnM

Comment 3

[[e-mail]]

Yup, that's exactly what happens.
Also to mention that setting gfx.webrender.compositor to false and restarting the browser fixes the issue. Probably some sort of regression similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1988422

Comment 4

[Laurențiu Nicola]

Dupe of #2026937

Comment 5

[:hello]

Out of curiosity do you also get split second pause/stutters at the start of every reel when scrolling reels on youtube and facebook?(desktop)
I noticed since 149 when im scrolling down reels on facebook the first second of a reel there's a split second pause/stutter.

It doesn't happen on reels I've already watched just new reels, so If I go back and forth to an old reel I already watched there's no split second pause/stutter.It only seems to happen to reels I haven't watched.

Only happens on firefox and wasn't a thing 5 days ago.I think it's related to 149

Comment 6

[Bob Hood [:bhood]]

Sotaro, since this is likely layer compositor, assigning to you for some attention.

Comment 7

[[e-mail]]

(In reply to :hello from comment #5)

Out of curiosity do you also get split second pause/stutters at the start of every reel when scrolling reels on youtube and facebook?(desktop)
I noticed since 149 when im scrolling down reels on facebook the first second of a reel there's a split second pause/stutter.

It doesn't happen on reels I've already watched just new reels, so If I go back and forth to an old reel I already watched there's no split second pause/stutter.It only seems to happen to reels I haven't watched.

Only happens on firefox and wasn't a thing 5 days ago.I think it's related to 149

Yup, it happens as well. This tends to be less of a problem if you disable the compositor. Definitely has to do with this. It's like if the browser just can't render whatever layer it has in that moment, or forgets whet it has been rendering in favor of another thing and just goes nuts.

Comment 8

[Sotaro Ikeda [:sotaro]]

Hi [e-mail], can you attach about:support taken after the problem happen?

Comment 9

[Anthony Kamau]

I'm on latest Firefox nightly 150.0a1 (2026-03-09) on Ubuntu 24.04.4 LTS fully patched.

I cannot zoom-in in Google maps - and very jittery.
I also cannot scroll in PDF's - also jittery as hell.

I was going to record a video of the issue and when I reduced my browser size to 1600 x 1280 (by chance), the issue disappeared.

If I increase browser size past 1800 x 1300, the stuttering returns.

This is a weird one!

Comment 10

[Anthony Kamau]

Something weird is going on.

After playing around with different resolutions of the browser window, I noticed that if I increase the resolution by small increments in either direction, I can get to past the resolution where the issue previously occurred (1800 x 1300) - now at 1914 x 1722 with no jittering screen.

I'll leave it to the experts to decipher that.

Comment 11

[Anthony Kamau]

Pardon the noise.

After realizing I hadn't closed my browser for a long while in order for snap to update it, I did an update to nightly 151.0a1 (2026-03-30) and now I can no longer replicate the issue.

Please ignore my previous verbiage.

Comment 12

[Sotaro Ikeda [:sotaro]]

With the STR of comment 0, mCompositionSurface->BeginDraw() in DCLayerCompositionSurface::Bind() sometimes caused the problem. When the problem happened, updateRect was empty. updateRect needs to be non empty.

Renderer::composite_simple() has the dirty rect empty check, but it did not work when the problem happened.

Comment 13

[[e-mail]]

Attachment: About Support RAW.txt

Comment 14

[[e-mail]]

Attachment: About Support Text.txt

Comment 15

[[e-mail]]

(In reply to Sotaro Ikeda [:sotaro] from comment #8)

Hi [e-mail], can you attach about:support taken after the problem happen?

Heya! Of course! here you are:

https://bugzilla.mozilla.org/attachment.cgi?id=9561149
https://bugzilla.mozilla.org/attachment.cgi?id=9561150

Comment 16

[Sotaro Ikeda [:sotaro]]

(In reply to [e-mail] from comment #15)

(In reply to Sotaro Ikeda [:sotaro] from comment #8)

Hi [e-mail], can you attach about:support taken after the problem happen?

Heya! Of course! here you are:

https://bugzilla.mozilla.org/attachment.cgi?id=9561149
https://bugzilla.mozilla.org/attachment.cgi?id=9561150

Thank you! The following error log seemed to be related to Bug 2028034.

Error: Handling webrender error 4

Comment 17

[[e-mail]]

(In reply to Sotaro Ikeda [:sotaro] from comment #16)

(In reply to [e-mail] from comment #15)

(In reply to Sotaro Ikeda [:sotaro] from comment #8)

Hi [e-mail], can you attach about:support taken after the problem happen?

Heya! Of course! here you are:

https://bugzilla.mozilla.org/attachment.cgi?id=9561149
https://bugzilla.mozilla.org/attachment.cgi?id=9561150

Thank you! The following error log seemed to be related to Bug 2028034.

Error: Handling webrender error 4

I see...
Just as a record, this problem is even more frequent on multimonitor configurations, but happens in any case.

Comment 18

[:hello]

(In reply to [e-mail] from comment #7)

(In reply to :hello from comment #5)

Out of curiosity do you also get split second pause/stutters at the start of every reel when scrolling reels on youtube and facebook?(desktop)
I noticed since 149 when im scrolling down reels on facebook the first second of a reel there's a split second pause/stutter.

It doesn't happen on reels I've already watched just new reels, so If I go back and forth to an old reel I already watched there's no split second pause/stutter.It only seems to happen to reels I haven't watched.

Only happens on firefox and wasn't a thing 5 days ago.I think it's related to 149

Yup, it happens as well. This tends to be less of a problem if you disable the compositor. Definitely has to do with this. It's like if the browser just can't render whatever layer it has in that moment, or forgets whet it has been rendering in favor of another thing and just goes nuts.

Thanks for the sanity check.
Guess il wait for a fix.

Comment 19

[Sotaro Ikeda [:sotaro]]

Hi [e-mail], can you check if the problem is addressed with latest nightly?

Comment 20

[[e-mail]]

Attachment: about support nightly RAW.txt

Comment 21

[[e-mail]]

Attachment: about support nightly Text.txt

Comment 22

[[e-mail]]

(In reply to Sotaro Ikeda [:sotaro] from comment #19)

Hi [e-mail], can you check if the problem is addressed with latest nightly?

Tested a few hours ago, the bug stopped happening, the browser even feels snappier for browsing, as it if rendered things faster than it did before. Yer magic man!

Comment 23

[[e-mail]]

Forgot to say I attached new about support files in case you nee dot review anything. There was something about the zero copy thing, but I guess maybe that's not important... maybe...

Comment 24

[Sotaro Ikeda [:sotaro]]

Great! Thank you for the checking.

Comment 25

[[e-mail]]

(In reply to Sotaro Ikeda [:sotaro] from comment #24)

Great! Thank you for the checking.

Yer most welcome dude!

Comment 26

[[e-mail]]

Oh BTW, what's the expected release version or milestone that will see this improvement? Just asking...

Comment 27

[Sotaro Ikeda [:sotaro]]

I am going to request uplift until release soon.

Comment 28

[[e-mail]]

Gotcha, thanks a lot for everything mate!