Thanks for the help Emilio! I've filed Bug 1890835 for the panel appearing on top of other windows, which most likely makes it clickable even though the windows prompt is open. Maybe fixing that bug will resolve the sec issue too.
Bug 1886082 Comment 20 Edit History
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Thanks for the help Emilio! I've filed Bug 1890835 for the panel appearing on top of other windows, which most likely makes it clickable even though the windows prompt is open. Maybe fixing that bug will resolve the sec issue too. Edit: It appears that this was a bug with my local profile. Potentially caused by some prefs I had not reset from testing. The PopupNotification is not on top when testing with a fresh profile. But it can still be clicked even when the window is in modal state.