In Configuration/General/Content Management, Enable WYSIWYG Editor is set as "Disabled by Default". And Use Static URLs for Media Content in WYSIWYG for Catalog is set as "No".
Everywhere in the admin panel (products, categories, pages..) the WYSIWYG Editor it's not working properly.
For example, if I go to a Product edit page to set the Description, all the HTML tags appear, and under the textarea it appears the button "WYSIWYG Editor". If I click it, it appears a Pop'up with the buttons "Show / Hide Editor" and Insert Image buttons at the top, and the text contains HTML elements.
See these images:
http://postimg.org/image/4831xzinl/
http://postimg.org/image/6pmkszjzb/
EDIT
For those who don't understand what I'm talking about: The editor worked before and now it doesn't work anymore! If I choose "Enabled by Default" / "Disabled by Default" the editor still does not apper. I haven't changed the core files. I thought that someone might know what can be the problem, but i can see that no one is able to post an answer (excepting Marius).
FIXED
The problem was that the hosting company removed some magento core files because "they contained viruses".. :) Some js files were deleted (tiny mce and others)