Overscan issue on macbook pro

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Hello, I've just installed F26 with default Gnome3(3.24.2) on macbook pro 13 2014 with retina,
plugging in an external monitor (dell u2414h - resolution 1920X1080) I'm facing a strange scaling issue:

default software such as terminal or nautilus scale correctly when moving to external screen,
instead downloaded apps (firefox/chrome/sublime) don't scale at all going from primary retina monitor to external dell monitor.

any help is greatly appreciated, regards from Italy.