Prior to macOS Sierra I would use
C-x 5 2 to create a separate frame which was created in an OS X window so that there were now two windows. This is using the latest EmacsForOSX version straight out of the box. Life was good.
I recently switched to macOS Sierra and discovered there is now a different behavior: after
C-x 5 2 the new window is turned into a tab inside the original Emacs frame (macOS window). An invisible frame at that if you are using macOS fullscreen mode. That sort of sucks.
Edit: Note that this behavior only exists in full screen mode so if you exit full screen mode C-x 5 2 does the right thing.
After playing around with the new macOS tab features I discovered that I could exit fullscreen mode to reveal the tabs and drag a tab out to create a separate Emacs frame. Life is better, however this is a rather clumsy way to get separate frames, for example, placed in each monitor on a dual monitor setup. Is there an easier way to achieve the pre-Sierra Emacs frame behavior in a post-Sierra world?
It strikes me that macOS Sierra breaks the legacy Emacs design decision that an Emacs frame can be modeled as an OS X/macOS window, therefore requiring code changes in Emacs to support the new macOS tab feature. Is anyone aware of Emacs development efforts to accept and deal with this?