"TinyMCE remove-base-64-image" immediately removes images dropped into the TinyMCE editor with Firefox and alerts the user with the reason.
Firefox allows a user to drag and drop an image from their desktop into the TinyMCE editor (Visual), where it is immediately converted to base64 code, which is undesirable as the image file size is much larger than the equivalent added by the standard WordPress method because...
'Sorry, dragging images into the editor is blocked as it will cause your webpages to load slowly, please use the "Add Media" button!'.
If you manage multiple WordPress sites this plugin will save you time checking if your clients are unwittingly crippling their page downloads.
A PixelTiger plugin.