If you have an attached Design in TinyMCE prefs, and it contains a stylesheet
with:
html { height: 100%; }
and you also have "Auto Resize" checked in TinyMCE prefs
The content block will infinitely grow in height while you are trying to edit a
page. Happens in Chrome, Safari, and Firefox (may need to clear browser cache to
test after making these setting changes).
In Edge, the content block doesn't grow, but it also has 0 height.