Rightclick, do not highlight textarea in webinspector

Browser: Firefox stable
When I rightclick in the editor on
http://codemirror.net/ and choose inspect element the textarea is highighted in the webinspector.
What setting can I use in order to highlight the span tag in the pre


We have to capture the right-click menu with the textarea to make copy/paste work. What does work is to first open the devtools, select the ‘picker’ tool from there, and then click on the editor.