On Serenity and on my Linux machine, we have a 1:1 CSS-to-device pixel
ratio. On macOS, we have a 2:1 ratio. This did not affect the Qt chrome,
because we are ignoring this position and placing the context menu at
the globally-accessible mouse position. The AppKit chrome will be using
this position, though.
This might be what caused the issue worked around by commit 8177ecb.