Magento - add WYSIWYG editor to custom widget

Question

I created a widget inside my custom module. Everything is working and the widget can be embedded onto CMS pages. However, instead of a textarea parameter type I want to add

Answer 1

I don't think this is compatible with Magento 1.9 anymore. I've tried this method and I keep getting a javascript error when saving the cms block / page where the widget is added

error: error in [unknown object].fireEvent(): event name: formSubmit error message: Cannot set property 'value' of null