If I understand correctly, this patch would mean that any window we don't explicit set `macnativefullscreen` on would now show the `+` icon and not maximize fully (over the dock etc), similar to how our old pre-native fullscreen mode used to work. Because there is built-in code in macOS that guesses when a window might want to do native full-screen, we could regress some windows/dialogs that used to be native fullscreen capable that won't be any more, but the green button UX will correctly reflect that. We need this to work around a crash due to a bug in the macOS internal machine, because we end up changing the state of these windows after creation due to how our window construction/property setting works. Firefox Enterprise is especially prone to triggering this bug.
Bug 2038980 Comment 4 Edit History
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If I understand correctly, this patch would mean that any window we don't explicit set `macnativefullscreen` on would now show the `+` icon and not maximize fully (over the dock etc), similar to how our old pre-native fullscreen mode used to work. Because there is built-in code in macOS that guesses when a window might want to do native full-screen, we could regress some windows/dialogs that used to be native fullscreen capable (but not marked by us as such) that won't be any more, but the green button UX will correctly reflect that. We need this to work around a crash due to a bug in the macOS internal machine, because we end up changing the state of these windows after creation due to how our window construction/property setting works. Firefox Enterprise is especially prone to triggering this bug.