saving in visual editor presents tiny confusing screens with unnecessary scrollbars. please increase them to full page. use case: add a reference. to check 5 clicks and scrolls are necessary, just to end up at a position where nothing can be changed.
In your screenshots, the diff window is already 900px wide; standard width, as used for the other windows, is 700px wide. I don't think going full-screen is a good outcome for users; it loses the anchoring to the context and the page flow, and encourages people to design/create/suggest layouts that are fundamentally incompatible with tablet and phone use.