User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0

Steps to reproduce:

On Dell Latitude E7250 (GPU Intel HD 5500) I've compared CPU usage while watching this Youtube video with Webrender and Direct3D 11 Compositing (gfx.webrender.force-disabled set to true).
https://www.youtube.com/watch?v=1La4QzGeaaQ

I've set 1080p 60fps quality with enhanced h-264ify plugin enabled however without this plugin (with software decoding) problem is also noticeable.

Actual results:

I've noticed significantly higher CPU usage on Webrender (default setting) than on Direct3D 11 compositing (option gfx.webrender.force-disabled set to true). I attach screenshoths with CPU usage graphs. I've marked with yellow color especially high CPU usage peaks on Webrender.

Expected results:

On Webrender CPU usage should be lower than on Direct3D 11 compositing.

Konrad, do you still see this problem?

Redirect a needinfo that is pending on an inactive user to the triage owner.
:gw, since the bug has recent activity, could you have a look please?

For more information, please visit auto_nag documentation.

This is impossible to check, beacause in the newest Firefox isn't possible to set Direct 3D acceleration.