Comment 145 for bug 52667

I tested with tbird 2.0.0.6 from ubuntu. I deactivated all my other plugins except enigmail to be sure and get the same result:
when using view->headers->normal headers the button is grey.
It doesn't matter whether you "expand" or "collapse" header in the mail window itself. Just the option in view menu has to be set.

John: Do you use enigmail or mnehy?

fabian