Scrolling apple.com today is very slow, mostly around the M1 graphic. It's smooth with WebRender disabled.

STR:

1. Enable WebRender (it is by default on this configuration) and restart
2. Visit apple.com
3. Scroll down to the M1 section and notice very slow speeds.
4. Disable WebRender and restart
5. Visit apple.com
6. Scroll down to the M1 section and notice scrolling remains smooth.

Expected:
Smooth scrolling, or at least WebRender on par with accelerated layers.

Actual:
Very slow scrolling on this machine with WebRender enabled.

Profiles:
WebRender enabled
WebRender disabled

Most of the time is being spent in update_texture_cache

The bottleneck is on the renderer thread which is spending most of its time uploading textures.

Sam, still seeing same slowness?

Since apple.com has changed significantly since the initial report, I loaded a copy from archive.org. I am still seeing slowness, but it's not nearly as rough as before. The profile also seems to look a bit different.

Here's a new profile: https://share.firefox.dev/3Inf7OA

I'm open to closing this if there isn't any obvious badness in the profile--while there is definite slowness, it seems to be doing about as well or better than Safari on this page. Unfortunately I cannot compare to accelerated layers any more.

The bug has a release status flag that shows some version of Firefox is affected, thus it will be considered confirmed.

Agreed, performance seems quite good on both the archived page and current version now. The only spike I noticed was a couple of frames of texture upload time.