1988728 - backdrop-filter: blur is laggy when GPU acceleration isn't available

Status: UNCONFIRMED

(Core :: Graphics: WebRender, defect, P2)

Description

[Samuel]

Attachment: firefox_backdrop_filter_blur.html

Steps to reproduce:

Using backdrop-filter: blur in Firefox when no GPU acceleration is available makes things extremely laggy. One common case where this happens is when running Firefox in a remote desktop session. Backdrop-filter blur works well without GPU acceleration on Chromium 140.

Open the attached HTML file and try to scroll to see the problem. By disabling backdrop-filter in the web inspector you can see that things start working normally again.

Issue seen on both Firefox ESR 128 on Red Hat Enterprise Linux 9 and in Firefox 142 on Fedora 42.

Actual results:

Scrolling on the website is very, very slow.

Expected results:

Things should work well, even on CPU fallback.

Comment 1

[Samuel]

Similar to this closed bug:

https://bugzilla.mozilla.org/show_bug.cgi?id=1718471

Comment 2

[Samuel]

I could not reproduce the issue on Fedora 42 with the nightly Firefox build downloaded directly from Mozilla. Could this be an issue with Red Hat's packaging or build of Firefox?

I also reported the issue to Red Hat:
https://bugzilla.redhat.com/show_bug.cgi?id=2395768

Comment 3

[BugBot [:suhaib / :marco]]

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

Comment 4

[Robert Longson [:longsonr]]

You can use the profiler https://profiler.firefox.com/ to determine what is slow. Compare the redhat to the nightly and see what stands out. If this is something only in the redhat packaged firefox then redhat will need to fix it.