[FIX] Destroy the editor properly. This prevents errors like

'this.getWindow(...).$ is undefined' in Firefox after closing
a popup containing an editor instance.
was opened in a popup window.

web_ckeditor4/static/src/js/web_ckeditor4.js

@@ -199,11 +199,16 @@ openerp.web_ckeditor4 = function(instance)
         {
             if(this.editor)
             {
-                CKEDITOR.remove(this.editor);
                 this.editor.removeAllListeners();
+                this.editor.destroy();
                 this.editor = null;
             }
         },
+        destroy: function()
+        {
+            this.destroy_content();
+            this._super();
+        },
         destroy_content: function()
         {
             this._cleanup_editor();