Currently, the GDK back-end is larger on OS X than the X11 when on a Retina display. This causes issues on my MacBook Pro with a smaller screen, with some windows being unusable or nigh-unusable.

When reporting a bug/issue:

• Screenshot

• The FontForge version and the operating system you're using
  Fontforge dad4fb5, Mac OS X 10.14.3
• The behavior you expect to see, and the actual behavior
  The X11 and GDK back-ends being the same size; The Mac version is noticeably bigger than the X11 version.