Similar to bug 1592026, but with the added challenge that the readback needs to be as low-overhead and "non-blocking" as possible.

We can likely enable our compositor work in Nightly before fixing this, we should not let it ride to release until we fix.

:mstange, is there a document about how to use "window recording"? I could not find it. The window recording was added by Bug 1536174.

• https://searchfox.org/mozilla-central/rev/923eec8d2fb8078ebc7a33a9e1ce73eac01f7446/browser/base/content/browser-sets.inc#336

It is used by browsertime when measuring "visual metrics" for pageload performance. But the simplest way to play with it is from the browser console. First, create a string pref with the name layers.windowrecording.path and set it to an absolute path to some directory. Then, restart Firefox, open the Browser Console (with devtools.chrome.enabled = true), and execute the following:

windowUtils.startCompositionRecording()
// now briefly interact with a web site in the browser, and then run:
windowUtils.stopCompositionRecording(true)

A new folder in the chosen directory should appear and be populated with PNG files which contain screenshots from the Firefox window.

Great! Thank you.

Depends on D59157

Depends on D59158

@Markus: Should this block Mac release?

Backed out for bustages on ScreenshotGrabber.h

Backout link: https://hg.mozilla.org/integration/autoland/rev/37eb71de7e8a1c16b2f222a14c9e91669ed49fbf
Log link: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=313709954&repo=autoland&lineNumber=20883

https://hg.mozilla.org/mozilla-central/rev/203d7e09574c
https://hg.mozilla.org/mozilla-central/rev/6b2299a3cd00
https://hg.mozilla.org/mozilla-central/rev/eb44242ad435

(In reply to Kris Taeleman (:ktaeleman) from comment #8)

@Markus: Should this block Mac release?

Yes, it should. It's causing confusion for users of the profiler, and sometimes even crashes.

The patches in this bug ended up only fixing the profiler screenshots aspect, and not the frame recording API. I filed bug 1664049 on the frame recording part.