Do you want to request a feature or report a bug?
BUG
What is the current behavior?
Editor will not initialise on Firefox
If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via fiddle.tinymce.com or similar.
https://codepen.io/dgrammatiko/pen/djNdGz
What is the expected behavior?
Editor should initialise normally
Which versions of TinyMCE, and which browser / OS are affected by this issue? Did this work in previous versions of TinyMCE?
TinyMCE 4.0.8, MacOS, Firefox 61