The answer to this question was originally posted here by Nikitas : fooobar.com/questions/925546 / ...
I copy the answer here for simplicity ...
After a little research, I found it.
1) Put this code in the .phtml file that you want the editor to display directly.
2) In the sixth line of code, you can see elements: "short_description" . You can change the "short_description" with the identifier of the element you want. You can add multiple item identifiers, separated by commas and without spaces.
Example: I put this code in app/design/adminhtml/default/default/template/catalog/product/edit.phtml because I want the editor to appear directly when I edit the product description, short description, etc.
The code:
<script type="text/javascript"> window.onload=function() { tinyMCE.init({ mode : "exact", elements: "short_description", theme : "advanced", plugins : "inlinepopups,style,layer,table,save,advhr,advimage,advlink,emotions,iespell,insertdatetime,preview,media,searchreplace,print,contextmenu,paste,directionality,fullscreen,noneditable,visualchars,nonbreaking,xhtmlxtras", theme_advanced_buttons1 : "newdocument,|,bold,italic,underline,strikethrough,|,justifyleft,justifycenter,justifyright,justifyfull,|,styleselect,formatselect,fontselect,fontsizeselect", theme_advanced_buttons2 : "cut,copy,paste,pastetext,pasteword,|,search,replace,|,bullist,numlist,|,outdent,indent,|,undo,redo,|,link,unlink,anchor,image,cleanup,help,code,|,insertdate,inserttime,preview,|,forecolor,backcolor", theme_advanced_buttons3 : "tablecontrols,|,hr,removeformat,visualaid,|,sub,sup,|,charmap,emotions,iespell,media,advhr,|,print,|,ltr,rtl,|,fullscreen", theme_advanced_buttons4 : "insertlayer,moveforward,movebackward,absolute,|,styleprops,|,cite,abbr,acronym,del,ins,|,visualchars,nonbreaking", theme_advanced_toolbar_location : "top", theme_advanced_toolbar_align : "left", theme_advanced_path_location : "bottom", extended_valid_elements : "a[name|href|target|title|onclick],img[class|src|border=0|alt|title|hspace|vspace|width|height|align|onmouseover|onmouseout|name],hr[class|width|size|noshade],font[face|size|color|style],span[class|align|style]", theme_advanced_resize_horizontal : 'true', theme_advanced_resizing : 'true', apply_source_formatting : 'true', convert_urls : 'false', force_br_newlines : 'true', doctype : '<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">' }); }; </script>