On 6 Jul 2017 1:53 p.m., "Alan Third" wrote: On 6 Jul 2017 12:29 p.m., "Paul Michael Reilly" wrote: I have recently switched to macOS Sierra and discovered that using C-x 5 2 to create a new frame works just fine, i.e. no different than OS X, if you do not enter full screen mode (via the green window decoration button). If you are in full screen mode C-x 5 2 is ignored, but if you then exit full screen mode it is clear that the second frame is now a tab (macOS Sierra tab feature). This behaviour should be fixed in master. Can you please try it? (nightly builds if you're using emacsformacos.com builds) I've just realised that we're using a build time version check, and the Emacs for macOS releases are built on an older version of macOS... I'm not sure what the best solution here is... I'll have a think about it.