Magento 1.9 – How to Enable WYSIWYG for Product Attribute Field

the error is due to Mage::getBaseUrl('media') does not pass the store parameter !

To solve this bug, change in :

app/code/core/Mage/Cms/Helper/Wysiwyg/Images.php

Find function : getImageHtmlDeclaration

and change :

$mediaPath = str_replace(Mage::getBaseUrl('media'), '', $fileurl);

by

$mediaPath = str_replace(mage::app()->getStore($this->_storeId)->getBaseUrl('media'), '', $fileurl);

There are several things to keep in mind when using WYSIWYG for transactional e-mails:

• Sending out HTML e-mails which can be viewed in a nice way in multiple e-mail clients is not always fun & easy: There are some "specialities" from mail client to mail client that need to be taken care of
• It could mess up your e-mail design and won't benefit some special adaptions as mentioned above
• You're limited to the WYSIWYG functions in your e-mail template. When I think of adding conditions like {{depend object.function()}} .... {{depend}} this can't be inserted with an WYSIWYG anyway.
• It will not work with responsive e-mail templates as you would not be able to edit reponsive e-mails with a WYSIWYG editor
• The WYSIWYG editor will try to interpret layout handles {{var items_html}} as widget instances which can cause problems (thanks to @SanderMangel for pointing that out).

I would not say that's impossible, if you find the ultimate WYSIWYG editor for transactional e-mails that does not cause problems, tell us :-)