I've seen this a few times now; Firefox 85b9. Windows just stop repainting. If the window loses/gains focus, it gets repainted properly once, but any interaction with the window doesn't draw anything.

M1 Mac Mini, default Firefox 85b9 config (installed yesterday). WebRender is enabled. I can't trigger it to happen on demand; things work fine for hours and then they don't. No crashes or anything; I can quit the browser just fine and things reopen properly when I relaunch.

Seems to be related to leaving Firefox alone for a while, and having the mac turn off the display; coming back to the computer I see the issue. I can't reproduce manually via Sleep or Screen Saver though, will see if it happens reliably again after display standby.

Definitely related to leaving the mac and letting things go into power save. If I leave my mac and go away for an hour, when I come back and unlock, Firefox will be in this state. New windows are also created in this state -- the initial repaint happens, but no updates after that.

Still happens with 86b1

Happens with:

• WebRender enabled or disabled (OpenGL compositing)
• Big Sur 11.1
• Big Sur 11.2 RC2 (20D62)

Graphics team thinks this might be in widget, and we don't have hardware. Wondering if the macos widget folks can help diagnose.