Overlay UI Spurious Appears Without User Input
Context: I'm fullscreen on MacOS Safari, on a Twitch stream.
The Bug: Periodically, the playback controls UI, including the progress bar, appear without any user interaction. They should stay invisible unless I move my mouse.
The cause: That chat window seems to instigate this issue. If I go out of fullscreen mode, and hide the chat view, and go back to fullscreen, the issue no longer occurs.