This morning, out of the blue, I received an Sorry, you need to enable sending referrers, for this feature to work error when trying to delete a duplicate comment. I haven’t made any recent changes to my installation of WordPress, I haven’t made any recent changes to Firefox including adding or deleting extensions, and I haven’t changed any settings in my firewall.
I checked the forums and found a solution for now.
In wp-admin/admin-functions.php I commented out the line
die(’Sorry, you need to enable sending referrers, for this feature to work.’); in the check_admin_referer() function.
I’m not sure what the implications are but I can now delete comments.