[Affected platforms]:
Platforms: Windows 8 / 8.1 , Windows 7, Ubuntu

[Preconditions]:

Reach about:config and set both gfx.webrender.enabled, gfx.webrender.software - true

[Steps to reproduce]:

1. Launch the Firefox browser.
2. Reach https://www.icelandicexplorer.com/ and scroll down.

Expected Result:
No visual issues should occur when scrolling the website.

Actual Results:
Some images overlap eachother when scrolling through the website.

Performance profile : https://share.firefox.dev/3fa96sh
Screen Recording: https://www.awesomescreenshot.com/video/3178149?key=bafbacba5c528b6c58c01d47a4bf8cd8

I'm not entirely sure if it should block Bug 1621376 since it happens without gfx.webrender.software enabled as well, but with the pref on its a lot more noticeable.

In SW-WR looks like a lot of time is spent in cs_clip_image. But as well, a really huge amount of time is spent in RenderDXGITextureHost::MapPlane. Matt and/or Sotaro?

Looks like this is WebGL readback performance.

Since sw-wr-perf-clip-image fixed the cs_clip_image issue, and we have other bugs on file for sw-wr-perf-d3d11-webgl, I am going to close this out.