Created attachment 150717 [details] blackpreview It appears in the latest unstable build, window previews are not working and instead are showing a black window. This happened on my Wayland session.
Cannot reproduce with a window thumbnail that shows a playing YouTube video. Were these windows showing videos from some source? Does it happen with Firefox windows playing video from other sources? Does it happen with any other windows?
duplicate of bug 455021
*** This bug has been marked as a duplicate of bug 455021 ***