User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:90.0) Gecko/20100101 Firefox/90.0

Steps to reproduce:

I enabled webrender software (so firefox is fast on bare metal and inside virtualbox) and browsed facebook.

Actual results:

After scrolling down for a while I noticed scrolling felt quite laggy - sometimes the page would flicker because it took so long to paint the content.

Please see the profile available at: https://share.firefox.dev/33DhJ7v

Expected results:

Webrender software should be almost as fast as the old "basic" backend.

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