Since updating WP to 3.6, FEE immediately inserts a blank image instead of showing the "add image" popup screen when clicking the "insert image" button.
I encounter this problem with the latest version of FEE but also with older versions.
Perhaps it has something to do with a jQuery conflict? Cf. http://wordpress.org/support/topic/troubleshooting-wordpress-36-master-list#post-4484014
Many thanks in advance for helping to sort this out.