I also have been having problems getting the WYSIWYG editor to display the Visual & Code tabs and the formatting icons in the Visual editor, despite disabling all the plugins, clearing the cache, enabling Javascript etc. I then did a clean install of a test blog and created a new blog database, and the problem disappeared. I suspected it may be due to file permissions, and I went back to my original blog and applied the permissions as described at https://codex.www.ads-software.com/Changing_File_Permissions. This fixed the problem. Also, the errors that were written to the Firefox error console disappeared. The permissions that I applied were (from the command-line in the blog root directory):
chmod -R 750 wp-includes
chmod -R 750 wp-admin
chmod -R 777 wp-content (maybe a bit overkill)
chmod 755 *.php
Don’t follow the above link’s instructions to chmod 666 index.php.
