I already tried all of the solutions you can find online like adding this to
1 define('CONCATENATE_SCRIPTS', false);
2 I also deactivated all plugins and changed the theme, still no dice
3 Verified that permissions are correct and visual editor is enabled
4 Tried replacing with other editor than TinyMCE, no dice
I suppose it is a server problem because another site on the server has the same problem.
Any suggestions how to debug it? "Add Media" works fine, so its not a JS issue or a permissions issue.
I believe it could be related to
mod_sec, but I disabled it and still no dice. Not sure where to begin the debugging process. Any suggestions?
Edit: I have found the problem, but no solution yet.
The following two lines are missing in the source on my broken server - on a working server they are not missing:
<div id="wp-content-editor-tools" class="wp-editor-tools hide-if-no-js"> <a id="content-html" class="wp-switch-editor switch-html" onclick="switchEditors.switchto(this);">Text</a> <a id="content-tmce" class="wp-switch-editor switch-tmce" onclick="switchEditors.switchto(this);">Visual</a>
Update: Apparently some people had luck disabling their antivirus, see here http://wordpress.org/support/topic/htmlvisual-missing-on-341-and-342