Doesn't work in WP 4.x #1
Description
WordPress 4.x changed the UI of the editor and the way that the Visual and HTML tabs work. This breaks the plugin.
The editor UI changes are in /wp-admin/js/editor.js
Specifically using the JS function
window.switchEditors.switchto( id )
button IDs are #tmce_content and #html_content
Look into a way of testing forWP >= 4.0 and using the JS instead of CSS.