Recently i have automatically upgraded my WordPress blog to the new release of WordPress 3.5. After that I can’t edit my post in Visual Editor mode. I have also confirmed that I have checked the Visual editor option in my profile. I have also tried disabling all plugins, switching to the default theme and delete browser cache, but still not worked. It give the same result, i still lost visual Editor Tab.
Solution for Lost Visual Editor :
The visual editor provides a semi-WYSIWYG (What You See is What You Get) content editor that allows you to easily create, edit, and format your blog content in a view similar to that of a word processor. If the default editing mode for WordPress it does not appear to be enabled, you can select the Visual tab in the top right corner of the editor area.
I found temporary solution in this forum, but i really worked for me. Hopefully the newer or future update of the WordPress version will fixed this issue..
Add this line Into the wp-config.php. Once you added this line, pleas try again whether the problem still exist or not.