When closing the File Browser window after making it fullscreen, Blender would
either crash or all windows would disappear, with no obvious way to bring them
back.
The "fix" is to not allow fullscreen for File Browsers (or any future "dialog"
windows), but only maximizing. From what I can tell that's how secondary
windows are supposed to work on macOS. What we previously did seemed like
something macOS doesn't handle cleanly, and I didn't find a simple way to do so
on our side.
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